Comparison of dye (oxazine and thiazine) materials as a photosensitizer for use in photogalvanic cells based on molecular interaction with sodium dodecyl sulphate by spectral study

The photochemistry of dye is playing a significant role for understanding the mechanism of electron transfer reactions in photoelectrochemical devices such as photogalvanic cells, DSSC, semiconductor photo-catalysis, photoconductors, etc. Oxazines (Brilliant Cresyl Blue and Nile Blue O) and thiazines (Azur A, Azur B, Azur C, Methylene Blue and Toluidine Blue O) dyes have been used widely as a photosensitizer with and without surfactants in the photogalvanic cells for solar power conversion and storage. Since, the stability and solubility of photosensitizers (dyes) are increased in the presence of surfactant and these properties lead to enhance the electrical output of the photogalvanic cells. Therefore, here we have studied the extent of interaction of different dyes with sodium dodecyl sulphate (SDS), find out the order of stability of dye–SDS on the basis of magnitudes of shifting in λ_max of dye monomer and try to correlate order of dye–SDS interaction with already reported electrical output data of photogalvanic cells. Brilliant Cresyl Blue, Nile Blue O, Azur A and TB O have shown red shifting while Azur B, Azur C and MB have shown blue shifting in their λ_max value with SDS, which indicates formation of dye–surfactant complex. But, the extent of formation of complex for different dyes with SDS was different due to change in their alkyl groups. Dyes with red shifting have greater stability in excited state as well as higher electrical output data of the cell than dye with blue shifting. On the basis of both red and blue shifting, order of stability of dyes–SDS complex was found as: Brilliant Cresyl Blue?>?Toluidine Blue O?>?Azur A?>?Nile Blue?>?Azur B?>?Methylene Blue?>?Azur C. The order of electrical output values of these dyes in photogalvanic cells have also been supported by literature data in the presence of SDS. Hence, the dye–surfactant complex which would have greater stability in excited state might be more useful for improvement of conversion efficiency and storage capacity of photogalvanic cells in the future.     

Solid-phase synthesis of quinoxaline derivatives using 6-amino-2,3-dichloroquinoxaline loaded on AMEBA resin

The solid-phase synthesis of quinoxaline derivatives 1 was accomplished through successive introduction of building blocks such as amines, methoxide, acid chlorides, and isocyanates into 6-amino-2,3-dichloroquinoxaline 2 loaded on AMEBA resin 3. The method made it possible to obtain the compound 1 in 63-100% purities and 36-89% isolated yields.     

Divergent synthesis of fused Benzo-xanthene and oxazine derivatives via Cu-catalyst

Cu-Cu₂O combination showed synergic effects in catalyzing intramolecular Ullmann coupling reaction for halo-Betti bases to afford fused benzo-xanthenes from both electron-rich and electron-deficient aromatic systems in good yield under mild reaction conditions. The sterically hindered halo-Betti bases also provided products in excellent yield. Under optimized condition, a gram scale reaction was also performed to afford the product in excellent yield. However, without ortho-halo substituted Betti-bases failed to afford fused benzo-xanthene derivatives. Exploring the reaction optimization without Cu metal, serendipitously it was produced 1,3-oxazine derivatives in excellent yield via intramolecular cross-dehydrogenative coupling (CDC) reaction. Similarly, electron-rich, electron-deficient and sterically hindered Betti-bases provided the products in good to excellent yield under mild condition.     

Solid-phase synthesis of substituted 3-amino-3′-carboxy-tetrahydrocarbazoles

Two related solid-phase synthesis routes have been developed allowing the synthesis of 3-amino-3′-carboxy substituted tetrahydrocarbazole derivatives. Diversity can be introduced at the amino and carboxy functionalities and at the nitrogen and the aromatic ring of the tetrahydrocarbazole moiety. Both routes rely on Fmoc-protected 1-amino-4-oxocyclohexanone carboxylic acid as central core element. Derivatization of the carboxy function is achieved with amines, derivatization of the amino functionality is possible by reaction with alkyl halides, isocyanates, activated alcohols, sulfonic acid chlorides or carboxylic acids. The tetrahydrocarbazole scaffold is generated by Fischer indole cyclization with phenyl hydrazine derivatives, thereby introducing diversity in the aromatic moiety. N-Alkylation at the indole nitrogen with alkyl halides delivers N-substituted derivatives.     

Efficient protocol for the synthesis of quinoxaline, benzoxazole and benzimidazole derivatives using glycerol as green solvent

A straightforward, efficient and more sustainable catalyst-free method has been developed for the synthesis of quinoxaline, benzoxazole, and benzimidazole ring system in glycerol to achieve yields that were comparable to or better than, those in conventional media. It is noteworthy that the reaction was exclusively carried out in glycerol-water system, rendering the methodology highly valuable from both environment and economic points of view.     

Bromination of quinoxaline and derivatives: Effective synthesis of some new brominated quinoxalines

The synthesis of brominated quinoxaline derivatives starting from several kinds of quinoxaline by different bromination strategies was studied. First the synthesis of some brominated quinoxalines was accomplished along with the development of an alternative and effective synthesis of some known compounds. A new, clean, and effective synthetic method for selective reduction of quinoxaline to 1,2,3,4-tetrahydroquinoxaline was also developed. The products obtained were characterized by means of NMR spectroscopy, elemental analyses, and mass spectrometry.     

First total synthesis of versicotide D and analogs

The first total synthesis of cyclotetrapeptide versicotide D has been achieved in 21% overall yield using solid phase peptide synthesis and solution cyclization. In addition, in the search for candidates of antimalarial new drugs, one cyclic tetrapeptide analog which differs in the sequence, and four cyclic pentapeptide containing N-methyl amino acids, were prepared. The obtained compounds were evaluated against P. falciparum 3D7. Versicotide D showed low micromolar antiplasmodial activity.     

Efficient solvent-free synthesis of pyridopyrazine and quinoxaline derivatives using copper-DiAmSar complex anchored on SBA-15 as a reusable catalyst

A catalytic system comprising mesoporous silica functionalized with Cu(II)-DiAmSar was synthe-sized. This was demonstrated as an efficient heterogeneous catalyst for the synthesis of biologically useful pyridopyrazine and quinoxaline heterocycles under solvent-free conditions. X-ray diffraction, transmission electron microscopy, N2 adsorption-desorption, Fourtier transformation infrared spectroscopy, and thermogravimetric analysis were used to characterize the catalyst and investi-gate the texture of SBA-15 during the grafting process.     

Solid-phase synthesis of peptide and glycopeptide thioesters through side-chain-anchoring strategies

An efficient new strategy for the synthesis of peptide and glycopeptide thioesters is described. The method relies on the side-chain immobilization of a variety of Fmoc-amino acids, protected at their C-termini, on solid supports. Once anchored, peptides were constructed using solid-phase peptide synthesis according to the Fmoc protocol. After unmasking the C-terminal carboxylate, either thiols or amino acid thioesters were coupled to afford, after cleavage, peptide and glycopeptide thioesters in high yields. Using this method a significant proportion of the proteinogenic amino acids could be incorporated as C-terminal amino acid residues, therefore providing access to a large number of potential targets that can serve as acyl donors in subsequent ligation reactions. The utility of this methodology was exemplified in the synthesis of a 28 amino acid glycopeptide thioester, which was further elaborated to an N-terminal fragment of the glycoprotein erythropoietin (EPO) by native chemical ligation.     

Solid-phase synthesis of biarylalanines via Suzuki cross-coupling and intramolecular N-acyliminium Pictet-Spengler reactions

Solid-supported masked peptide aldehydes containing 3- or 4-iodophenylalanine residues were subjected to Pd-catalyzed Suzuki cross-coupling reactions with arylboronic acids. The biarylalanines generated were applied in intramolecular N-acyliminium Pictet-Spengler reactions. In this way, a range of pharmacologically interesting aryl-substituted pyrroloisoquinolines was obtained in excellent purity (>95%).     

Solid-phase synthesis of α-substituted proline hydantoins and analogs

The manual solid-phase preparation of racemic α-substituted bicyclic proline hydantoins and analogs, which can potentially contain up to four sites of structural diversity (ring size and substitution on the ring or at the ring fusion), is described. Key steps involved alkylation of aldimines of resin-bound amino acids with α,ω-dihaloalkanes and intramolecular displacement of the halide to generate α-substituted prolines and homologs. After formation of resin-bound ureas by reaction of these sterically-hindered secondary amines with isocyanates, base-catalyzed cyclization/cleavage yielded the desired hydantoin products.     

Construction of mononuclear transition metal(II) complexes with bi- and tridentate,neutral hydrazone ligands with a quinoxaline hub

A series of Co(II), Ni(II), Cu(II), and Zn(II) complexes of bi- and tridentate hydrazones were prepared. Ligands L¹ and L² were synthesized by the condensation of 2-mercapto-3-hydrazinoquinoxaline with 2-hydroxy-3-formylquinoline and 3-acetylcoumarin, respectively. The compounds were characterized by various spectro-analytical techniques and magnetic moment studies. The complexes are found to be monomeric and non-electrolytes. In these complexes, [CuL¹Cl₂] has square pyramidal geometry and others have octahedral. The copper complexes are electrochemically active in the applied potential range.     

Solid-phase extraction in the determination of gold, palladium, and platinum

A simple classification of various sorbents and solid-phase extraction procedures used for preconcentration of trace levels of Au, Pd, and Pt from different sample types is proposed in this review article. The large variety of available sorbents/procedures has been organized according to expected mechanisms of sorption process (complex formation; ion exchange; adsorption; ion-imprinted or molecularly imprinted polymers); according to the kind of monomeric units of the polymer matrix as well as on the basis of the kind of functional group responsible for main performance characteristics (selectivity, capacity) of the sorbent. Advantages of chemically modified sorbents, sulfur-containing sorbent extractants, and ion-imprinted polymers, together with rational pretreatment by means of microwave treatments, scaling down of enrichment, and quantification by means of flow and flow injection approaches are given. Preferred instrumental techniques for quantification of ppb levels of Au, Pd, and Pt in prepared concentrates/column eluates are multielement instrumental techniques: inductively coupled plasma optical emission spectrometry (ICP-OES), and inductively coupled plasma mass spectrometry (ICPMS). Excellent limits of detection at picogram levels of these analytes are provided by electrothermal atomic absorption spectrometry (ETAAS), generally in single-element mode and the neutron activation analysis (NAA), while X-ray fluorescence spectrometry and flame AAS are rarely applied because of lack of sensitivity at sub-ppm levels of Au, Pd, and Pt. Some problems of atomic spectrometric quantification techniques and their representative limits of detection are given. Recent applications to geological, industrial, pharmaceutical, biological, and other materials are tabulated. References have been selected mostly from the period 1995 to 2010.     

Solid-phase synthesis of dihydrovirginiamycin S1, a streptogramin B antibiotic

We describe the first solid-phase synthesis of dihydrovirginiamycin S(1), a member of the streptogramin B family of antibiotics, which are nonribosomal-peptide natural products produced by Streptomyces. These compounds, along with the synergistic group A components, are "last line of defense" antimicrobial agents for the treatment of life-threatening infections such as vancomycin-resistant enterococci. The synthesis features an on-resin cyclization and is designed to allow production of streptogramin B analogues with diversification at positions 1', 1, 2, 3, 4, and 6. Several synthetic challenges known to hinder the synthesis of this class of compounds were solved, including sensitivity to acids and bases, and epimerization and rearrangements, through the judicious choice of deprotection conditions, coupling conditions, and synthetic strategy. This work should enable a better understanding of structure-activity relationships in the streptogramin B compounds, possible identification of analogues that bypass known resistance mechanisms, and perhaps the identification of analogues with novel biological activities.     

Solid-phase supported nitrosocarbonyl intermediates: Old scope and new limitations in the organic synthesis

Nitrosocarbonyl intermediates on solid polystyrenic support are generated at room temperature by the mild oxidation of resin-bound stable nitrile oxides. They undergo one-pot ene reactions with tetramethyl- and trimethyl-ethylene and other highly substituted olefins. Less substituted ethylenes as well as cyclohexene and cyclopentene are heavily disfavoured and nitrosocarbonyls on solid phase undergo fast dimerization and/or decomposition pathways. These outcome strongly limit the SP applications in organic synthesis, although applicable to structurally specific N-alkenyl hydroxamic acids.     

Synthesis,crystal structure and negative hyperconjugation study of quinoxaline derivatives containing piperazine

The negative hyperconjugation (NHC) of sp² and sp³ hybrid nitrogen atoms were studied based on the calculation of quinoxaline derivatives containing piperazine moiety. The energy level, electronic density and spatial position of acceptor orbital are all important factors of NHC. NHC of nitrogen atom does not limit in the case that the σ*-acceptor orbital is in the anti-staggered positon of donor orbital, but it will switch off when nitrogen atom loses its lone pair electron. These results are proved by the crystal structure and the calculation of vibration frequencies. At last, two quinoxaline derivatives synthesized in this work show good anticancer activities against leukemia cell lines.     

Solid-phase oligosaccharide synthesis of a small library of N-glycans

Solid-phase oligosaccharide synthesis is based on a hydroxymethylbenzyl benzoate spacer linker which is connected to the Merrifield resin (1 P). Glycosylation was performed with O-glycosyl trichloroacetimidates of glucosamine, mannose, and galactose permitting chain extension (2e, 5e), branching (4b, 7b, 8b), and chain termination (3t, 6t, 9t) with the use of O-benzyl, O-benzoyl, and N-dimethylmaleoyl as permanent and O-fluorenylmethoxycarbonyl (Fmoc) and O-phenoxyacetyl (PA) as temporary protecting groups. The steps required on solid phase are i) glycosylation under TMSOTf catalysis, ii) selective cleavage of the temporary protecting groups, Fmoc with NEt3 and PA with 0.5 equivalents of NaOMe in CH2Cl2/MeOH, and iii) product cleavage from the resin with 4.0 equivalents of NaOMe in CH2Cl2/MeOH and following O-acetylation for convenient product isolation. Thus a highly successful synthesis of a small library of seventeen N-glycan structures was made possible comprising the N-glycan pentasaccharide core structure 53 and two further chain extended hexa- and heptasaccharide N-glycans with a glucosamine or a lactosamine residue, respectively, which is attached to one of the mannose residues of the core structure (56 and 59).     

Solid-phase synthesis of （Z）-allyl iodides from 3-acetoxy-2-methylene-alkanoates with recyclable polymer-supported selenium bromide

Reaction of polystyrene-supported lithium selenide with 3-acetoxy-2-methylene-alkanoates afforded the corresponding allyl selenide resins and subsequent cleavage from the polymer by treating with methyl iodide to furnish(Z)-allyl iodides in good yields and high purities.The polymeric selenium reagent can be regenerated and reused.So it is a environmentally benign reagent.     

Solid-phase extraction and simultaneous spectrophotometric determination of trace amounts of Co, Ni and Cu using partial least squares regression

A novel sensitive and simple method for rapid extraction, preconcentration and determination of cobalt, nickel and copper as their 1-(2-pyridilazo)-2-naphthol (PAN) complexes using polytetrafluoroethylene filter as solid phase and multivariate calibration of spectrophotometric data is presented. The analytical wavelengths of 400-700 nm were chosen and the experimental calibration matrix for partial least squares (PLS) was designed with 21 samples of 5.90-41.25, 0.30-29.35 and 0.64-41.30 ng ml⁻¹ for cobalt, nickel and copper, respectively. The cross-validation method was used for selecting the number of components. The root-mean-square errors of predictions (RMSEPs) were between 0.48 and 1.37 ng ml⁻¹. In this work we could reach preconcentration factors of 100 or even higher by using polytetrafluoroethylene as solid phase which is cheap and can be used in a wide range of pH, flow rates and for many times. The proposed method was successfully applied to the simultaneous determination of Co, Ni and Cu in tap and pit water samples.