Cationic Reagents Research Articles

ChemInform Abstract: Evidence for a Bis(alkylidene)silacyclopropane Intermediate in the Platinum-Mediated Formation of a Silacyclobutene.

When Ph 2 Si(C≡CMe 3 ) 2 is treated with a cationic Pt-H reagent, a 4-alkylidene-1-silacyclobutenyl ring system is formed. Evidence for the presence of two intermediates in this reaction sequence is obtained by using selective trapping reactions. Acetic acid cleaves at Pt-C bond to give alkenylsilane products, indicating the intermediate formation of a Pt, Si-μ-alkenylidene complex. ROH reagents react with a proposed bis(alkylidene)silacyclopropane intermediate to initiate ring opening and to form η 3 -butadienyl complexes (where R=H, Me, Et, or Ph)

ChemInform Abstract: Assessing the Superelectrophilic Dimension Through σ‐Complexation, SNAr and Diels—Alder Reactivity

AbstractReview: 183 refs.

Cysteine accessibility analysis of the human alpha7 nicotinic acetylcholine receptor ligand-binding domain identifies L119 as a gatekeeper

A large number of structurally diverse ligands have been produced to selectively target α7 nicotinic acetylcholine receptors (nAChRs). We applied the method of scanning cysteine accessibility mutations (SCAM) to the ligand-binding domain of the α7 nAChR to identify subdomains of particular importance to the binding and subsequent activation by select agonists. We evaluated the activity of four structurally distinct α7 agonists on wild-type human α7 and 44 targeted mutants expressed in Xenopus oocytes. Responses were measured prior and subsequent to the application of the sulfhydryl reagent methanethiosulfonate ethylammonium (MTSEA). One mutant (C116S) served as a Cys-null control, and the additional mutants were made in the C116S background. In many cases, the insertion of free cysteines into the agonist-binding site had a negative effect on function, with 12 of 44 mutants showing no detectable responses to ACh, and with only 19 of the 44 mutants showing sufficiently large responses to permit further study. Several of the cysteine mutations, including W55C, showed selectively reduced responses to the largest agonist tested, 2-methoxy,4-hydroxy-benzylidene anabaseine. Interestingly, although homology models suggest that most of the introduced cysteine mutations should have had good solvent accessibility, application of MTSEA had no effect or produced only modest changes in the agonist response profile of most mutants. Consistent with previous studies implicating W55 to play important roles in agonist activation, MTSEA treatment further decreased the functional responses of W55C to all the test agonists. While the cysteine mutation at L119 itself had relatively little effect on receptor function, treatment of L119C receptors with MTSEA or alternative cationic sulfhydryl reagents profoundly decreased activation by all agonists tested, suggesting a general block of gating. The homologous mutation in heteromeric nAChRs produced similar results, provided that the mutation was placed in the beta subunit complementary surface of the ligand-binding domain. Structural models locate the L119 residue directly across the subunit interface from the C-loop of the primary face of the binding domain. Our data suggest that a covalent modification of L119C by MTSEA or other cationic reagents might block the binding of even small agonists such as TMA through electrostatic interactions. Reaction of L119C with small non-polar reagents increases activation by small agonists but can block the access of large ligands such as benzylidene anabaseines to the ligand-binding domain.

Solvent selection for matrix-assisted laser desorption/ionization time-of-flight mass spectrometric analysis of synthetic polymers employing solubility parameters

The principle relating to the selection of a proper matrix, cationization reagent, and solvent for matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) of synthetic polymers is still a topic of research. In this work we focused on the selection of a suitable MALDI solvent. Polystyrene PS7600 and poly(ethylene glycol) PEG4820 were analyzed by MALDI-TOF MS using various solvents which were selected based on the Hansen solubility parameter system. For polystyrene (PS), dithranol was used as the matrix and silver trifluoroacetate as the cationization reagent whereas, for poly(ethylene glycol) (PEG), the combination of 2,5-dihydroxybenzoic acid and sodium trifluoroacetate was used for all experiments. When employing solvents which dissolve PS and PEG, reliable MALDI mass spectra were obtained while samples in non-solvents (solvents which are not able to dissolve the polymer) failed to provide spectra. It seems that the solubility of the matrix and the cationization reagent are less important than the polymer solubility.

Investigating the Effect of Mixing Ratio on Molar Mass Distributions of Synthetic Polymers determined by MALDI-TOF Mass Spectrometry using Design of Experiments

It is well known that the mixing ratio affects the molar mass distribution of synthetic polymers determined by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). Surely, the molar mixing ratio determines whether a mass spectrum will be obtained or not. However, depending on the mass range, several effects such as multimer formation occur, which might be a source of errors in molar mass distribution calculations. In this study, the effect of mixing ratio was investigated for several synthetic polymers, including polystyrene (PS), poly(dimethylsiloxane) (PDMS), poly(ethylene glycol) (PEG), and poly(methyl methacrylate) (PMMA) using statistical designs of experiments. The 2(3) full factorial design was found to be suitable in the study of more than 1000 samples. The obtained MALDI mass spectra as well as the ANOVA statistics show that the mixing ratio affects the molar mass distribution. The optimal mixing ratio for a defined synthetic polymer depends on the studied combination (matrix, cationization reagent, solvent).

Inhibition of the expression and function of TRPV4 by RNA interference in dorsal root ganglion

Background: Transient receptor potential vanilloid 4 (TRPV4) calcium channel is an essential mediator of spinal nociceptive transmission in dorsal root ganglion (DRG), but its mechanism in pain transmission is poorly understood. The present study intended to evaluate the effect of small interfering RNA (siRNA) on the expression and function of TRPV4 in DRG neurons and its possible usage in pain relief treatment.Methods: Two pairs of siRNA targeting TRPV4 (siRNAa and siRNAb) were designed and synthesized. A mismatched double-strand RNA was chosen as negative control. siRNAs were transfected into primary culture DRG neurons with cationic lipid-based CodeBreaker reagent. Real-time reverse transcription polymerase chain reaction and Western blot analysis were performed to assess the change of TRPV4 messenger RNA (mRNA) and protein expression in DRG. Calcium imaging and ELISA of substance P were carried out to evaluate the function change of TRPV4. The relationship between TRPV4 and PKC was also observed by immunocytochemistry.Results: TRPV4 mRNA levels in DRG of mismatch and control groups were significantly higher (3·88- and 3·75-fold) than normal. However, siRNAa and siRNAb increased only 1·26- and 1·87-fold, respectively. TRPV4 protein expression was also decreased significantly, as indicated by Western blot. In addition, the function of TRPV4 as ion channel was evaluated by calcium imaging and P substance release before and after siRNA treatment. Inhibition of TRPV4 activity was observed after transfection with both siRNA sequences. Protein kinase C expression, which was thought to be related with TRPV4 function, was inhibited as well.Conclusion: TRPV4 is a key component in hypotonic signal transduction, and designed siRNA inhibits mRNA level, protein expression and function of TRPV4 in DRG neurons. Therefore, synthesized siRNA is suggested to be a potential treatment for TRPV4-related pathological conditions, specifically pain.

Negative Electron Transfer Dissociation of Deprotonated Phosphopeptide Anions: Choice of Radical Cation Reagent and Competition between Electron and Proton Transfer

Despite significant developments in mass spectrometry technology in recent years, no routine proteomics sequencing tool is currently available for peptide anions. The use of a molecular open-shell cation is presented here as a possible reaction partner to induce electron transfer dissociation with deprotonated peptide anions. In this negative electron transfer dissociation (NETD) scheme, an electron is abstracted from the peptide anion and transferred to the radical cation. This is demonstrated for the example of the fluoranthene cation, C(16)H(10)(+*), which is reacted with deprotonated phosphorylated peptides in a 3-D ion trap mass spectrometer. Selective backbone cleavage at the C(alpha)-C bond is observed to yield a and x fragments, similarly to electron detachment dissociation (EDD) of peptide anions. Crucially, the phosphorylation site is left intact in the dissociation process, allowing an identification and localization of the post-translational modification (PTM) site. In contrast, NETD using Xe(+*) as the reagent cation results in sequential neutral losses (CO(2) and H(3)PO(4)) from a/x fragments, which complicate the interpretation of the mass spectra. This difference in dissociation behavior can be understood in the framework of the reduced recombination energy of the electron transfer process for fluoranthene, which is estimated at 2.5-4.5 eV, compared to 6.7-8.7 eV for xenon. Similarly to ETD, proton transfer is found to compete with electron transfer processes in NETD. Isotope fitting of the charge-reduced species shows that in the case of fluoranthene-mediated NETD, proton transfer only accounts for <20%, whereas this process highly abundant for Xe(+*) (43 and 82%). Since proton abstraction from Xe(+*) is not possible, this suggests that Xe(+*) ionizes other transient species in the ion trap, which then engage in proton transfer reactions with the peptide anions.

Nucleophilic cationization reagents.

Nucleophilic cationization reagents fitted with aminooxy groups are described. Practical syntheses of mono- and bis-aminooxy tetraalkylammonium iodides including N-hydroxyethyl-functionalized analogs are reported. An oximation example using one of the reagents is presented to illustrate their use in synthesis of cationic materials.

Assessing the superelectrophilic dimension through σ-complexation, SNAr and Diels–Alder reactivity

In the domain of organic chemistry, S(N)Ar substitutions represent a class of reactions of overwhelming importance, both in synthesis and in the understanding of structure-reactivity relationships, especially the role of sigma-complex intermediates. The primary factor necessary for achievement of S(N)Ar reactions is the presence of a good leaving group, which allows facile rearomatization of the ring undergoing nucleophilic attack. Consistent is the finding that the superelectrophilic chloronitrobenzofuroxans--or furazans--exhibit a very high S(N)Ar reactivity, allowing a number of C-C, C-N, C-O couplings to be achieved that are not accessible with the classical series of nitro-substituted aromatics. Of particular interest is the synthesis of a number of indoles, indolizines, pyrroles and extended pi-excessive aromatic structures like azulene substituted by superelectrophilic moieties. The remarkable driving force for the facile completion of these reactions is the 10 orders of magnitude greater reactivity of 10pi-electron-deficient heteroaromatics such as 4,6-dinitrobenzofuroxan (DNBF) than of the most reactive trinitrobenzene derivatives in sigma-adduct complexation. Among the factors that have been recognized as governing superelectrophilicity, there is the poor aromaticity of 6-membered 10pi-electron structures investigated, with a common origin for sigma-complexation and pericyclic processes. A remarkable capacity of these structures is actually to contribute to a variety of Diels-Alder reactions. As an example, the DNBF molecule formally behaves as a nitroalkene, being susceptible to act as a dienophile as well as a heterodiene. Another remarkable Diels-Alder pathway is the capacity of the 6-membered carbocyclic ring of DNBF to act as a carbodiene. Also noteworthy is the successful Diels-Alder trapping of the dinitroso intermediate associated with 1-oxide/3-oxide tautomerism of the furoxan moiety of 4-aza-6-nitrobenzofuroxan. A point of fundamental importance in taking advantage of the reactivity of superelectrophilic structures at hand has been a successful calibration of their reactivity within the electrophilicity E scale developed by Mayr to describe nucleophile-electrophile combinations in general. It has thus been established that the E parameters measuring the electrophilicity of neutral heteroaromatics lie in the same region of the E scale as a number of highly reactive cationic reagents. Besides a reactivity rather similar to that of the 4-nitrobenzenediazonium cation (vide supra), the most electrophilic neutral molecules (DNBF, DNTP, DNBZ) are as electrophilic as tropylium cations or a number of metal-coordinated carbenium ions. Furthermore, there is a remarkable link between the pK(a)(H(2)O) and E scales, as evidenced by the existence of a unique linear relationship spanning more than 20 orders of reactivity. This relationship appears as being a nice probe to predict the feasibility of S(N)Ar substitutions and related sigma-complexation processes. Also revealing in terms of feasibility of the reactions is the existence of a close correlation between the electrochemical oxidation potential E degrees of sigma-adducts and their positioning on the pK(a)(H(2)O) scale. Our data can also be used to evaluate the potential of a theoretical model recently derived from DFT calculations, namely the global electrophilicity index omega, for the description of nucleophile-electrophile combinations. While showing several significant deviations, a reasonably linear omega vs. pK(a)(H(2)O) relationship is obtained when restricting the correlation to structurally similar electrophilic moieties. On this basis, valuable information could be derived regarding the polar character of some DA reactions. Overall, the global electrophilicity (omega) approach may be a promising avenue in future work of electrophile-nucleophile combinations.

Preparation and application of a new cationic starch ether – Starch–methylene dimethylamine hydrochloride

A new cationic starch ether – starch–methylene dimethylamine hydrochloride (SMMAHC) was synthesized by the reaction of corn starch with cationic reagent hydroxymethyl dimethylamine hydrochloride (HMMAHC) using dry process according to Mannich reaction. Reaction parameters (temperature, time, molar ratio of HMMAHC to anhydrous glucose unit (AGU) of starch, and content of HMMAHC) and their effects on the degree of substitution (DS) and reaction efficiency (RE) had been investigated. Under the optimal reaction conditions, SMMAHC with high DS of 0.79% and RE of 96.3% was obtained. The structures of SMMAHC were characterized by 13C-NMR and DEPT-135 spectroscopy. SMMAHC was used as flocculant to treat dyestuff (reactive brilliant red KE-3B) wastewater. The effects of DS and pH on the flocculation were studied and the dyestuff flocculation value reached a maximum of 209 mg/g.

Dinuclear metal(II) complexes of polybenzimidazole ligands as carriers for DNA delivery

A metal-based nonviral carrier for DNA-transfer in gene therapy was synthesized and characterized. The strong intermolecular π–π contacts are common in the observed dinuclear Cu 2+ and Co 2+ complexes of polybenzimidazole ligands. The affinity assays indicated that the strong binding of the complexes to DNA is driven by both electrostatic attractions between the complexes and DNA and the intercalation of the ligands between DNA base pairs. The typical in vitro studies showed that micromolar doses of each complex tested can efficiently and rapidly condense free DNA, either in linear or circular state, from solutions into well defined and globular nanoparticles with varied sizes. Therefore, the formation and dissociation of the DNA condensates were explored in detail under different conditions, indicating that the sizes of DNA condensates can be regulated by changing both doses and incubation time for the different dinuclear complexes. Since the intermolecular π–π interactions in the DNA-bound complexes may be a key force to drive DNA condensation, we propose a new DNA condensation model that is essentially distinct from that proposed for the most studied multivalent cationic reagents used in DNA condensation. The cellular uptake experiments successfully performed with the DNA condensates including plasmid pGL3 control vector that strongly expresses luciferase in many types of mammalian cells, as well as cytotoxicity evaluation, demonstrated the potentiality of the dinuclear metal(II) complexes as a new nonviral gene carrier. Finally, the dinuclear Co 2+ complexes of polybenzimidazole ligands are suggested to be the most potential nonviral gene carriers that are not impacted by serum proteins.

Cationic tamarind kernel polysaccharide (Cat TKP): A novel polymeric flocculant for the treatment of textile industry wastewater

Synthesis of cationic tamarind kernel polysaccharide (Cat TKP), its detailed physicochemical characterization and application as an efficient flocculant for the treatment of textile industry wastewater have been investigated. N-3-Chloro-2-hydroxypropyl trimethyl ammonium chloride (CHPTAC) was used as a cationic reagent to introduce quaternary amine groups onto the backbone of tamarind kernel polysaccharide (TKP). Various grades were synthesized to obtain the optimized one. Effect of reaction parameters onto the degree of cationization has also been investigated. The synthesized polymers were characterized by various macromolecular characterization techniques, which confirm that cationization does take place. Afterwards, the applicability of TKP and various grades of Cat TKP's as flocculants for the treatment of textile industry wastewater was investigated. The flocculation experiments showed that TKP alone contributes little to the flocculation. However, cationic TKP led to significant improvement as flocculant for the treatment of textile industry wastewater. The best performing Cat TKP (i.e. Cat TKP 3) was thereafter compared with a commercial flocculant, which is cationic in nature. It has been observed that Cat TKP 3 surpasses the flocculation efficiency over commercial flocculant.

Recovery of Silica from the Sumikawa Geothermal Fluids by Addition of Cationic Reagents

Recovery of Silica from the Sumikawa Geothermal Fluids by Addition of Cationic Reagents

Introducing Transition-Metal Complex Together with Conjugated Ligand into Polymeric Iodoplumbate: Structure Characterization, Properties and Theoretical Study of a New Semi-Conductive Hybrid: {[Cu(II)(2,2′-bipy)3][Pb2I6]} n

A new hybrid coordination polymer {[Cu(II)(2,2′-bipy)3][Pb2I6]} n (1) was synthesized by the reaction of Cu(NO3)2, 2,2′-bipy, PbI2 and NaI in DMF/DMSO mixed solvent. As revealed by X-ray structural analysis, 1 consists of [Pb2I6] 2− polyanions and discrete [Cu(II)(2,2′-bipy)3]2+ structure-directing agent cations. The polymeric negative chain [Pb2I6] 2− is built up by face-sharing of PbI6 octahedra. Structure-directing reagent cations and polymeric negative chains are in combination with each other by static attracting force to form so-called hybrid structure. Experimental and theoretical optical property investigations indicate that 1 possesses semiconductor property. DFT calculation was executed to probe the electronic structure of 1. To our interest, when using both second metal and π system as electronic tuning species, conjugated system is more preferable. A new hybrid coordination polymer introduced transition-metal complex together with conjugated ligand was synthesized. Interestingly, when using both second metal and π system as electronic tuning species, conjugated system is more preferable.

Preparation of cationic cotton with two-bath pad-bake process and its application in salt-free dyeing

Cationic cotton was prepared by a designed two-bath pad-bake process with 3-chloro-2-hydroxypropyltrimethylammonium chloride as cationizing reagent to realize recycle utilization of the reagent and continuous processing of cationization. Experiments showed that 8.0% (o.w.bath) of the reagent, 1:1 of molar ratio of sodium hydroxide to the reagent, 60 °C and 6 min of baking temperature and time were selected for cationization and the obtained cationic cotton was suitable for application in salt-free reactive dyeing. The structures of both the untreated and cationic fibers were investigated by X-ray diffraction and scanning electronic microscopy. Higher dye utilization and color yields could be realized on the cationic cotton than that on the untreated one in the conventional dyeing. Levelness dyeing and good fastness properties of the dyes on the cationic fabrics were obtained. Besides, colorimetric properties and mechanical strength of the dyed fabrics were both evaluated to show applicability of this preparation process of cationic cotton.

Determination of Cu(III) in semiconductor ceramics using cationic violet reagent

A method is presented for the determination of Cu(III) ion in semiconductor ceramic materials. It is based on (a) the reaction of copper(III) with Fe(II) ions, (b) the quantitative formation of Fe(III) ions, (c) liquid-liquid extraction of Fe(III) in the form of an ion associate between the FeCl4- anion with a Cationic Violet dye, and (d) spectrophotometric quantitation of the ion associate. All processes are executed in a single sequence of steps. The absorbance of the colored extracts obeys Beer's law in the range from 0.16 to 1.92 mg L−1 of Cu(III). The molar absorptivities range from 38,000 to 82,000 L mol−1 cm−1 depending on the kind of extractant used. The effects of other ions on the recovery of Cu(III) were studied, and those that generally occur with copper in semiconductor samples do not interfere.

Supramolecular assemblies of zwitterionic nanoliposome-polynucleotide complexes as gene transfer vectors: Nanolipoplex formulation and in vitro characterisation

Synthetic gene transfer vectors based on zwitterionic nanoliposome-DNA assemblies (nanolipoplexes), formed by the mediation of magnesium ions, were prepared by a scalable method without employing volatile solvents, high-shear force treatments or extrusion. The zwitterionic nanolipoplexes (NLP) were formulated with PC (phosphatidylcholine) and DPPC (a natural lung surfactant) incorporating different amounts of cholesterol (CHOL). The resulting structures were characterised in terms of their morphology, size and DNA content. In addition, the toxicity and transfection efficiency of the nanolipoplexes were evaluated in cultured Chinese hamster ovary-K1 (CHO-K1) cells. The effects of the multivalent cation Mg2+ on nanoliposome-DNA transfection potency were evaluated. Formulations containing 10% CHOL showed maximum transfection efficiency and the optimum amount of Mg2+ ions for transfection with minimum cytotoxicity was ca. 20 mM. The zwitterionic formulations showed significantly less cytotoxicity compared to a commercially available cationic liposome reagent or polyethylenimine (PEI) while they were superior in terms of gene transfer potency. The zwitterionic vectors formulated in this study avoid the use of toxic cationic lipids as well as toxic solvents and may have potential application in gene therapy. The new method will enable scale-up and manufacture of safe and efficacious transfection vehicles required for preclinical and clinical studies. Based on the advantages and superiority of the formulated nanolipoplexes, this method allows for the acceleration of nanolipoplex formulation, enabling the rapid development and evaluation of novel carrier systems for genes and other drugs.

Optimized Basic Conditions Are Essential for Successful siRNA Transfection into Primary Endothelial Cells

RNA interference (RNAi) is a powerful technique in basic research and has a high potential for therapeutic applications. To realize its clinical applicability, introduction of short double-stranded RNA (dsRNA) has to be carried out under physiological conditions. This study evaluates two cationic liposomal transfection reagents on the efficiency of successful silencing of primary human endothelial cells. Transfection efficiency was investigated under different conditions, for example different media during transfection, duration of transfection, siRNA concentration, and the use of serum and antibiotics. Viability after transfection was examined by CASY and MTT assay. Interferon response was examined by real-time PCR. First we revealed that transfection carried out in the presence of serum and antibiotics caused good knockdown results only by the use of the novel lipid cationic transfection reagent. Both lipid cations had slightly the same transfection efficiency over the range of 10-150 nM siRNA concentration. Examination of interferon response showed increasing OAS1 and STAT1 expression, but not as high as if the transfections were carried out with synthetic polyinosinic-polycytidylic acid double-stranded RNA (poly[IC]). The optimized combination of basic conditions for transfection significantly enhanced the efficiency of the siRNA-mediated knockdown, without causing toxicity or stimulation of the interferon pathway.

884. A Novel Class of Rigid, Cationic Nucleic Acid Transfection Reagents Based on Carotenoid Lipids

884. A Novel Class of Rigid, Cationic Nucleic Acid Transfection Reagents Based on Carotenoid Lipids

Antioxidant Hydroquinones Substituted by β-1,6-Linked Oligosaccharides in Wheat Germ

Seven new compounds that demonstrate antioxidant properties, 4-hydroxy-3-methoxyphenyl beta-d-glucopyranosyl-(1-->6)-beta-D-glucopyranosyl-(1-->6)-beta-D-glucopyranoside (1), 4-hydroxyphenyl beta-D-glucopyranosyl-(1-->6)-beta-D-glucopyranosyl-(1-->6)-beta-D-glucopyranoside (2), 4-hydroxy-3-methoxyphenyl beta-D-glucopyranosyl-(1-->6)-beta-D-glucopyranosyl-(1-->6)-beta-D-glucopyranosyl-(1-->6)beta-D-glucopyranoside (3), 4-hydroxy-3-methoxyphenyl beta-D-glucopyranosyl-(1-->6)-beta-D-glucopyranoside (4), 4-hydroxy-3,5-dimethoxyphenyl beta-D-glucopyranosyl-(1-->6)-beta-D-glucopyranoside (5), 4-hydroxy-3,5-dimethoxyphenyl beta-D-glucopyranosyl-(1-->6)-beta-D-glucopyranosyl-(1-->6)-beta-D-glucopyranoside (6), and 4-hydroxy-2-methoxyphenyl beta-d-glucopyranosyl-(1-->6)-beta-D-glucopyranosyl-(1-->6)-beta-D-glucopyranoside (7), were isolated from wheat germ. The structures were determined by spectroscopic and chemical methods. Compound 1 was the most abundant, approximately 2 mg isolated from each gram of wheat germ. The antioxidant activity of compounds 1-7 was determined by the Trolox equivalent antioxidant capacity assay, and 2 and 7 showed higher values than the other compounds. Compounds 1 and 3-6 reacted with the radical cation reagent within a few seconds, whereas 2 and 7 required several minutes for complete reaction. Compound 1 was shown to protect plasmid DNA from oxidative stress damage caused by hydrogen peroxide; this effect was concentration-dependent.