Pyridine Solution Research Articles

HPLC method for Residual 2-Bromoethylamine Hydrobromide in Hemoglobin-based Oxygen Carriers Derived with 4-Methoxybenzenesulfonyl Chloride

A stable high-performance liquid chromatography-UV (HPLC) method was developed for the separation and quantification of residual 2-bromoethylamine hydrobromide (BEA) in hemoglobin-based oxygen carriers (HBOCs). Residual BEA was derived by 4-Methoxybenzenesulfonyl chloride (MOBS-Cl) at 20 °C for 5 min in a pyridine solution. With this organic reaction system, MOBS-Cl hydrolysis in aqueous phase can be avoided in the process of derivatization, and glycine (Gly), a protein stabilizer, does not dissolve and extract from the organic reaction system, thus avoiding the serious interference of Gly on BEA determination. After derivatization, the derivative product was analyzed by HPLC with a mobile phase of 35% acetonitrile and 65% 0.01 mol/L ammonium acetate solution (v:v) and detected at 240 nm. The linear range was 0.41–40.98 μg/mL, with a correlation coefficient R2 of >0.9976. Excellent method reproducibility was observed by intra- and inter-day precision, with a relative standard deviation of <3%. The detection limit (S/N = 3) was found to be <0.02 μg/mL. This method can be used for routine determination of residual 2-bromoethylamine hydrobromide in hemoglobin-based oxygen carriers and other biological medicines. The proposed method also provides a new strategy for the separation and determination of other amino compounds which can dissolve in organic phase.

Electrochemical stripping of cotton fabrics dyed with Reactive Black 5 in water and wastewater

Cotton fabrics dyed with Reactive Black 5 (RB5) was electrochemically stripped using Ti/TiO2-RuO2-IrO2 anode in water, pyridine and phenol solution. The results showed that RB5 dye could be easily stripped from the surface of cotton fabrics through the cleavage of chromophoric group (NN) under the attack of hydroxyl radicals (OH) and active chlorines generated in situ. Efficient stripping performance could be obtained in water and pyridine solution, whilst the stripping percent was not obviously affected by pyridine concentration and layers of dyed cotton fabrics. Whereas, phenol existing in water slowed the stripping rate due to the competition between the stripping of RB5 dye and the degradation of phenol. In the case of multi-layer dyed cotton fabrics, the stripping performance of the inner layer is superior to that of the outer layer owing to that the cotton fabrics hinder the diffusion of active chlorines and OH. The FTIR analysis of stripped cotton fabrics showed that the effect of electrochemical process and the existence of pollutant in water on the stripped cotton fabrics could be negligible. Electrochemical oxidation could also successfully strip various dyes from waste cotton fabrics in the investigated stripping solutions. Therefore, electrochemical oxidation provides an environmentally friendly alternative for color stripping of dyed cotton fabrics. The removal of dye from cotton fabrics and the degradation of pollutant in water could occur simultaneously, implying that wastewater containing chloride ions may replace the fresh water as stripping solution.

Intermolecular Interactions of Pyridine in Liquid Phase and Aqueous Solution Studied by Soft X-ray Absorption Spectroscopy

Abstract Intermolecular interactions of pyridine in liquid and in aqueous solution are studied by using soft X-ray absorption spectroscopy (XAS) at the C, N, and O K-edges. XAS of liquid pyridine shows that the N 1s→π* peak is blue shifted and the C 1s→π* peak of the meta and para sites is red shifted, respectively, as compared with XAS of pyridine gas. These shifts in liquid are smaller than those in clusters, indicating that the intermolecular interaction of liquid pyridine is weaker than that of pyridine cluster, as supported by the combination of quantum chemical calculations of the core excitation and molecular dynamics simulations of the liquid structure. On the other hand, XAS spectra of aqueous pyridine solutions (C5H5N)x(H2O)1−x measured at different molar fractions show that in the pyridine rich region, x&gt;0.7, the C and N 1s→π* peak energies are not so different from pure liquid pyridine (x=1.0). In this region, antiparallel displaced structures of pyridine molecules are dominant as in pure pyridine liquid. In the O K-edge XAS, the pre-edge peaks sensitive to the hydrogen bond (HB) network of water molecules show the red shift of −0.15 eV from that of bulk water, indicating that small water clusters with no large-scale HB network are formed in the gap space of structured pyridine molecules. In the water rich region, 0.7&gt;x, the N 1s→π* peaks and the O 1s pre-edge peaks are blue shifted, and the C 1s→π* peaks of the meta and para sites are red-shifted by increasing molar fraction of water. The HB network of bulk water is dominant, but quantum chemical calculations indicate that small pyridine clusters with the HB interaction between the H atom in water and the N atom in pyridine are still existent even in very dilute pyridine solutions.

Synthesis and Optical Properties of Phenanthroline-Derived Schiff Base-Like Dinuclear RuII -NiII Complexes.

Two phenanthroline-derived Schiff base-like ligands with a covalently linked ruthenium(II) phosphorescent unit were synthesised and converted into bimetallic RuII -NiII complexes. The optical properties were studied to examine a possible photoluminescence quenching through a nonradiative energy-transfer upon a coordination-induced spin-state switch (CISSS) at the nickel(II) centre. Therefore, the metalloligands and the nickel(II) complexes were studied using UV/Vis absorbance, steady-state, and time-resolved emission spectroscopy in solutions of MeCN and pyridine. It is demonstrated that the nature of the bridging ligand between the ruthenium(II) donor and the nickel(II) acceptor strongly influences the photophysical behaviour upon CISSS. For the complex with a phenazine bridge, photoluminescence quenching is observed in the presence of a paramagnetic nickel(II) centre.

Hydrogen-bonding-directed helical nanofibers in a polythiophene-based all-conjugated diblock copolymer.

One-dimensional (1D) helical nanofibers were prepared through the self-assembly of an achiral all-conjugated diblock copolymer, poly(3-hexylthiophene)-b-poly[3-(6-hydroxyl)hexylthiophene] (P3HT-b-P3HHT) in an aged pyridine solution. Such helical nanofibers were formed by the π-π interaction between planar rigid polythiophene backbones cooperating with the hydrogen-bonding interactions between the polar hydroxyl groups of the side chains of polythiophenes. Intriguingly, the Young's modulus of such helical fibers is as high as ∼5.16 GPa, which is about twice that of P3HT films characterized by the peak force quantitative nanomechanical (PF-QNM) method. Furthermore, for the first time, we report that such helical fibers based on all-conjugated polythiophenes exhibited a relatively high field-effect mobility of 0.03472 cm2 V-1 s-1. This work provides a promising approach to craft crystalline helical nanostructures based on polythiophenes possessing both superior mechanical and good charge transport properties, which has great potential for application in other π-conjugated systems or building blocks for complex superstructures, and mechanical and optoelectronic devices.

Modeling Spin Interactions in a Triangular Cobalt(II) Complex with Triaminoguanidine Ligand Framework: Synthesis, Structure, and Magnetic Properties.

The new tritopic triaminoguanidine-based ligand 1,2,3-tris[(pyridine-2-ylmethylidene)amino]guanidine (H2pytag) was synthesized. The reaction of a mixture of cobalt(II) chloride and cobalt(II) perchlorate with the ligand H2pytag in pyridine solution leads to the formation of the trinuclear cobalt(II) complex [Co3(pytag)(py)6Cl3]ClO4. Three octahedrally coordinated high-spin cobalt(II) ions are linked through the bridging triaminoguanidine backbone of the ligand leading to an almost equilateral triangular arrangement. The magnetic properties of the complex were investigated by magnetic measurements, variable-temperature, variable-field magnetic circular dichroism (MCD) spectroscopy, and density functional theory as well as ab initio calculations. A rather strong antiferromagnetic exchange interaction between the cobalt(II) centers of ca. -12 cm-1 is determined together with a strong local anisotropy. The single-ion anisotropy of all three cobalt(II) centers is found to be easy-plane, which coincides with the tritopic ligand plane. MCD measurements and theoretical investigations demonstrate the presence of rhombic distortion of the local Co surrounding.

Heterobimetallic 3d-4f (Zn/La) {6,6′-Dimethoxy-2,2′-[naphthalene-2,3-diylbis(nitrilomethylidyne)]diphenolato}-pyridylzinc(II)-tris(nitrato-O,O′)lanthanum(III) Monohydrate

Herein, we report the synthesis and structural characterization of a complex with extended aromaticity based on a naphthalene-bridged Schiff base complex with two metal binding pockets. In a first step, the Zn(II) complex (ZnL), {6,6′-dimethoxy-2,2′-[naphthalene-2,3-diylbis(nitrilomethylidyne)]diphenolato}a-pyridylzinc(II) was isolated followed by refluxing with lanthanum(III) nitrate to produce the heterobimetallic complex {ZnL[La(NO3)3·H2O]}. Crystals suitable for X-ray diffraction were grown by vapor diffusion of THF into a pyridine solution of the complex. The monoclinic unit cell (P21/n) is commensurately modulated along the c-axis direction and contains four crystallographically independent molecules with pseudo-translational symmetry being broken by slightly differing orientations of included pyridine and THF solvate molecules. The zinc atom adopts a distorted square pyramidal geometry and sits slightly above the ligand plane, whereas the lanthanum atom adopts an all-face capped trigonal prismatic geometry and sits below the ligand plane. Structural characterization of this diamagnetic complex lays the groundwork for applying these synthetic techniques to the near-infrared emitting lanthanides for practical application.

Molecular Dynamics and Neutron Scattering Studies of Mixed Solutions of Caffeine and Pyridine in Water.

Insight into the molecular interactions of homotactic and heterotactic association of caffeine and pyridine in aqueous solution is given on the basis of both experimental and simulation studies. Caffeine is about 5 times more soluble in a 3 m aqueous pyridine solution than it is in pure water (an increase from ∼0.1 m to 0.5 m). At this elevated concentration the system becomes suitable for neutron scattering study. Caffeine-pyridine interactions were studied by neutron scattering and molecular dynamics simulations, allowing a detailed characterization of the spatial and orientational structure of the solution. It was found that while pyridine-caffeine interactions are not as strong as caffeine-caffeine interactions, the pyridine-caffeine interactions still significantly disrupted caffeine-caffeine stacking. The alteration of the caffeine-caffeine stacking, occasioned by the presence of pyridine molecules in solution and the consequent formation of heterotactic interactions, leads to the experimentally detected increase in caffeine solubility.

Reductive Disproportionation of CO2 with Bulky Divalent Samarium Complexes

The base-free divalent samarium complex Cptt2Sm (1; Cptt = 1,3-(tBu)2(C5H3)) has been synthesized in diethyl ether by salt metathesis of SmI2. Crystals of 1 suitable for X-ray study have been obtained by sublimation at 116 °C under reduced pressure. The dissolution of 1 in thf and pyridine solution leads to the solvent adducts Cptt2Sm(thf)2 (3) and Cptt2Sm(py) (4), respectively, while drying 3 under reduced pressure yields CpttSm(thf) (5). The reaction of CO2 with the base-free divalent samarium complexes Cptt2Sm (1) and Cpttt2Sm (2; Cpttt =1,2,4-(tBu)3(C5H2)) leads to the clean formation of bridged carbonate samarium dimers [Cpttt2Sm]2(μ-CO3) (7) and [Cptt2Sm]2(μ-CO3) (8). This is indicative of the reductive disproportionation of CO2 in both cases with release of CO. This contrasts with the formation of the oxalate-bridged samarium dimer reported from the reaction of CO2 with the Cp*2Sm(thf)2 complex. Otherwise, the reaction with CO does not proceed with the bulky complexes, while traces of O2 have led t...

A Terminal Iron(IV) Nitride Supported by a Super Bulky Guanidinate Ligand and Examination of Its Electronic Structure and Reactivity.

Utilizing the bulky guanidinate ligand [LAr*]- (LAr* = (Ar*N)2C(R), Ar* = 2,6-bis(diphenylmethyl)-4-tert-butylphenyl, R = NCtBu2) for kinetic stabilization, the synthesis of a rare terminal Fe(IV) nitride complex is reported. UV irradiation of a pyridine solution of the Fe(II) azide [LAr*]FeN3(py) (3-py) at 0 °C cleanly generates the Fe(IV) nitride [LAr*]FeN(py) (1). The 15N NMR spectrum of the 115N (50% Fe≡15N) isotopomer shows a resonance at 1016 ppm (vs externally referenced CH3NO2 at 380 ppm), comparable to that known for other terminal iron nitrides. Notably, the computed structure of 1 reveals an iron center with distorted tetrahedral geometry, τ4 = 0.72, featuring a short Fe≡N bond (1.52 Å). Inspection of the frontier orbital ordering of 1 shows a relatively small HOMO/LUMO gap with the LUMO comprised by Fe(dxz,yz)N(px,y) π*-orbitals, a splitting that is manifested in the electronic absorption spectrum of 1 (λ = 610 nm, ε = 1375 L·mol-1·cm-1; λ = 613 nm (calcd)). Complex 1 persists in low-temperature solutions of pyridine but becomes unstable at room temperature, gradually converting to the Fe(II) hydrazide product [κ2-(tBu2CN)C(η6-NAr*)(N-NAr*)]Fe (4) upon standing via intramolecular N-atom insertion. This reactivity of the Fe≡N moiety was assessed through molecular orbital analysis, which suggests electrophilic character at the nitride functionality. Accordingly, treatment of 1 with the nucleophiles PMe2Ph and Ar-N≡C (Ar = 2,6-dimethylphenyl) leads to partial N-atom transfer and formation of the Fe(II) addition products [LAr*]Fe(N═PMe2Ph)(py) (5) and [LAr*]Fe(N═C═NAr)(py) (6). Similarly, 1 reacts with PhSiH3 to give [LAr*]Fe[N(H)(SiH2Ph)](py) (7) which Fukui analysis shows to proceed via electrophilic insertion of the nitride into the Si-H bond.

The magnetic exchange interaction in bi- and tetranuclear copper(II) complexes with the bis-azomethine of 1,3-diaminopropanol-2 and 4-hydroxy-3-formylcoumarin with an azide exogenous bridge

By the reaction of Cu(II) perchlorate with the condensation product of 1,3-diamino-2-propanol and 4-hydroxy-3-formylcoumarin (H3L) in the presence of sodium azide, a tetranuclear copper(II) complex with the composition [Cu2L(μ2-1,1-N3)]2 (I) was obtained. On crystallization from a pyridine solution, the crystalline adduct [Cu2L(μ2-N3)(py)2] (II) (py=pyridine) was obtained and further characterized by XRD. The copper ions in (II) are coordinated by ONO’NO donor atoms of the triply deprotonated pentadentate ligand and the azide anion is coordinated in an asymmetric µ2-1,1 fashion, favoring a “roof”-like conformation of the molecule. The pyridine molecules are coordinated to each copper center, completing the distorted square-pyramidal coordination environment, but in a different way – for one copper ion the solvent molecule populates an apical position, for the other – a position in the basal plane. The tetranuclear complex is formed by linking two binuclear [Cu2L] units by two bridging μ2–1,1–N3 groups in a head-to-tail fashion. The temperature dependence of the magnetic susceptibility was studied for both I and II samples, showing a medium strength overall antiferromagnetic exchange for I and a weak ferromagnetic one with 2J=+5cm−1 for II. Two major superexchange pathways in I – through an alkoxide oxygen atom of the polydenate ligand and through the bridging azide-anion are characterized by opposite magnetic interaction characters – antiferromagnetic (2JO=−328cm−1) and ferromagnetic (2JN=+132cm−1), correspondingly. Quantum-chemical modeling using the broken symmetry approach was performed for II and possible binuclear isomers of I, differing in the azide-anion coordination mode and conformation of the polydentate ligand, and for two possible tetranuclear dimers.

Heteroleptic Complexes of the Tridentate Pyridine‐2,6‐di‐tetrazolate Ligand

AbstractThe synthesis and spectroscopic characterisation of a series of heteroleptic complexes of the tridentate pyridine‐2,6‐di‐(5‐tetrazolate) (pydtz2−) with Co(II), Ni(II), Cu(II) and Zn(II) and pyridine (Py) and H2O as coligands is reported. Single crystal XRD data reveals the formation of octahedrally configured complexes [Co(pydtz)(H2O)(Py)2], [Co(pydtz)(H2O)2(Py)]⋅2H2O, [Ni(pydtz)(Py)3]⋅2Py, and [Zn(pydtz)(H2O)(Py)2]⋅Py, and a markedly Jahn‐Teller distorted octahedral structure for [Cu(pydtz)(H2O)2(Py)]. Magnetic measurements reveal a S = 3/2 high‐spin configuration for the Co(II) complex [Co(pydtz)(H2O)(Py)2], an S = 1 ground state for the Ni(II) derivative and S = 1/2 Cu(II) ions for [Cu(pydtz)(H2O)2(Py)], the latter is supported by electron‐paramagnetic‐resonance spectroscopy. The crystalline materials are subject to severe corrosion as revealed by powder XRD and DSC‐TG experiments. H2O and pyridine co‐crystallisates and coligands are easily cleaved. At the same time DSC‐TG reveal very high stability of the [M(pydtz)] fragments with exothermic decomposition at T &gt; 300 °C. As a consequence, in pyridine solution in all cases the species [M(pydtz)(Py)3] are observed. Ultraviolet‐visible light absorption spectroscopy reveals a strong ligand field procured by the pydtz2− ligand and electrochemical measurements suggest very strong σ‐donation but only weak π‐accepting abilities of pydtz2− compared to the isostructural terpy (2,2’;6’,2’’‐terpyridine) ligand.

Electrospinning of gelatin with tunable fiber morphology from round to flat/ribbon

The electrospinning of gelatin with tunable fiber morphology from round to flat/ribbon was shown, and the detailed studies were conducted to correlate the fiber morphology with electrospinning process parameters and gelatin concentration in electrospinning solution. Particularly, variations in the applied voltage and the concentration of gelatin led to the transition of fiber shape from round to flat/ribbon. The formation of flat-shaped fibers was attributed to rapid evaporation of the solvent (formic acid) from the fiber matrix with increasing the applied voltage and gelatin concentration. On the other hand, round fibers were due to the steady evaporation of formic acid throughout the cross-section of fibers. WAXS analysis revealed that the loss of triple-helical crystalline structure in gelatin after the electrospinning process. The gelatin fibers were cross-linked through treatment with toluene 2,4-diisocyanate (TDI) in a mixed solution of acetone and pyridine, and XPS confirmed the cross-linking of the fibers over an increased carbon content on the elemental composition of the fiber surface due to the incorporated TDI moieties. Overall, this study focuses on morphological tuning of gelatin electrospun fibers towards a flat/ribbon-like structure by variation of electrospinning parameters and polymer concentration, and thus, the proposed concept can be adapted towards flattened/ribbon-like fibers of other protein-based systems by electrospinning.

Activated carbon from sugarcane bagasse ash for melanoidins recovery

This work investigates the value added utilization of two sugar-distillery wastes: (i) melanoidins, which are complex Maillard reaction products in molasses distillery wastewater, and (ii) unburnt carbon in sugarcane bagasse ash. Activated unburnt carbon (AUC), prepared by deashing and steam activation, had properties comparable to commercial activated carbon (CAC). Both carbons are suitable for melanoidins adsorption followed by desorption using 25% pyridine solution. For AUC, the equilibrium adsorption data is well described by Langmuir isotherm up to 35 °C while Freundlich model fits better at higher temperature. Adsorption using CAC followed Freundlich isotherm at all temperatures. Both carbons followed pseudo second order kinetics and displayed endothermic physisorption. Recovery of melanoidins from AUC (78%) was close to that observed with CAC (80%).

Preparation and Characterization of Group 13 Cyanides.

Binary Group 13 cyanides [PPh4 ][Ga(CN)4 ], [PPh4 ]2 [In(CN)5 ], and [PPh4 ]2 [Tl(CN)5 ] were obtained in quantitative yields from the corresponding metal trifluorides MF3 (M=Ga, In, Tl) by fluoride-cyanide exchange reactions with Me3 SiCN in the presence of stoichiometric amounts of [PPh4 ]CN in acetonitrile solution. The 2,2'-bipyridine (bipy) adducts [(bipy)2 Ga(CN)2 ][Ga(CN)4 ], [(bipy)In(CN)3 ], and [(bipy)Tl(CN)3 ] were obtained from the reaction of MF3 with Me3 SiCN and bipy in acetonitrile. While the reaction of the metal trifluorides with Me3 SiCN in acetonitrile resulted in recovery of the starting materials, the reaction of MF3 with Me3 SiCN in pyridine (py) solution resulted in the formation of the pyridine adducts [(py)2 Ga(CN)3 ], [(py)3 In(CN)3 ], and [(py)2 Tl(CN)3 ]. The cyano compounds were characterized by their vibrational spectra and, in most cases, by their X-ray crystal structures.

Effect of VBC-1814/7J, a poly-phytocompound, on a non-infectious model of pharyngitis.

Pharyngitis presents as an inflammation of the oropharynx, and clinical examination often shows evidence of nasopharyngitis. In numerous cases the condition occurs as a self-limiting illness of non-infectious aetiology, whose clinical management remains a matter for debate given the inappropriateness of antibiotics, the reported worsening following steroid use and the recent discouragement of the use of Chinese herbal medicine. The aim of the present study was thus to test VBC-1814/7J, a poly-phytocompound with known anti-inflammatory and immune-response enhancing properties, in an experimental model of non-infectious pharyngitis. Experimental non-infectious pharyngitis was induced by applying a pyridine solution to the surface of the pharyngeal mucosa in rats that were either normally fed (group A) or fed VBC-1814/7J three days prior to and three days subsequent to the induction of pharyngitis (group B). Healthy rats treated with topical saline were used as a control (group C). At time-points of 0, one hour, one day and three days sacrifices were carried out and microscopic examination, Evans blue (EB) dye extravasation and tissue concentrations of tumour necrosis factor (TNF)-α, interleukin (IL)-6 and mRNA of α- and β-defensins were studied. As compared with group C, group A showed significant microscopic damage, EB extravasation, and increases in the levels of TNF-α and IL-6, as well as in the mRNA of three defensins (P<0.001) on the third day of observation. VBC-1814/7J significantly mitigated these microscopic and inflammatory markers while allowing a prompter and wider defensin reaction (P<0.05 vs. group A). These data suggest that VBC-1814/7J, as demonstrated in earlier studies, has the potential to address non-infectious pharyngitis in clinical practice.

Optical and conductive properties of functional materials extracted from coal tar pitches treated by air oxidization method

The oligomers having the blue photoluminescence and conductivities of 5 × 10–7–7.4 × 10–4 S m–1 after doping by iodine are extracted successfully from coal tar pitches which were dealt with by the air oxidization method at 350°C. Meanwhile, it is observed that extracted materials have the blue photoluminescence with the fluorescence quantum yield of 7–10.2%. In these cases, we used the solutions of toluene and pyridine to extract these functional materials from coal tar pitches. Consequently, we consider these extracted materials showing the advantages in the application of fabricating the electronic devices, because it can decrease the production cost remarkably than use of the materials obtained by general organic synthesis methods. Finally, this research also can provide the one of beneficial references for solving the serious problem of overproduction of coal tar pitches in China. The oligomers having the blue photoluminescence and conductivities of 5 × 10–7–7.4 × 10–4 S m–1 after doping by iodine are extracted successfully from coal tar pitches which were dealt with by the air oxidization method at 350°C. Meanwhile, it is observed that extracted materials have the blue photoluminescence with the fluorescence quantum yield of 7–10.2%. In these cases, we used the solutions of toluene and pyridine to extract these functional materials from coal tar pitches. Consequently, we consider these extracted materials showing the advantages in the application of fabricating the electronic devices, because it can decrease the production cost remarkably than use of the materials obtained by general organic synthesis methods. Finally, this research also can provide the one of beneficial references for solving the serious problem of overproduction of coal tar pitches in China.

Phase equilibria and critical phenomena in the cesium nitrate–water–pyridine ternary system

The solubilities of components, phase equilibria, and critical phenomena in the cesium nitrate–water–pyridine ternary system are studied in the 5–100°C temperature range by the visual–polythermal method. Cesium nitrate is found to exhibit a salting-out effect at temperatures above 79.9°C causing phase separation in homogeneous water–pyridine solutions. The temperature of formation of the critical monotectic tie line (79.9°C) and the compositions of solutions corresponding to the liquid–liquid critical points at three temperatures are determined. The pyridine distribution coefficients between the aqueous and organic phases of the monotectic state at 85.0, 90.0, and 100.0°C are calculated. Their values demonstrate that salting-out of pyridine from aqueous solutions by cesium nitrate increases at higher temperatures. The plotted isotherms of phase diagrams confirm the fragment of the scheme of topological transformation of the phase diagrams of salt–binary solvent ternary systems with salting-in and salting-out phenomena.

Homo-C-nucleoside analogs IV. Synthesis of 4-(2,5-anhydro-D-altro-pentitol-1-yl)-2-phenyl-2H-1,2,3-triazole homo-C-nucleoside. CD assignment of the absolute configuration of the carbon bridge.

Dehydrative cyclization of 4-(D-altro-pentitol-1-yl)2-phenyl-2H-1,2,3-triazole in basic medium with one moler equivalent of p-toluene sulfonyl chloride in pyridine solution gave the homo-C-nucleoside 4-(2,5-anhydro-D-altro-1-yl)-2-phenyl-2H-1,2,3-triazole. The structure and anomeric configuration was determined by acylation, nuclear magnetic resonance (NMR), and mass spectroscopy. The stereochemistry at the carbon bridge of homo-C-nucleoside 2-phenyl-2H-1,2,3-triazoles was determined by circular dichroism (CD) spectroscopy.

Acid-base properties of tetrapyrazinoporphyrazines. 1. Deprotonation of octaethyltetrapyrazinoporphyrazine in CH2Cl2, THF, DMSO and pyridine. The crucial role of water

Combination of experimental and theoretical methods were used to study NH-acidity and related spectral properties of tetrapyrazinoporphyrazines – octaazaanalogues of phtalocyanines. The theoretical values of deprotonation enthalpy (DPE) in gaseous phase indicate that substitution of benzene rings in phthalocyanine by pyrazine fragments strongly enhances the NH-acidity of the macrocycle which can be further tuned by introduction of substituents in pyrazine rings. Spectrophotometric titration study of octaethyl substituted tetrapyrazinoporphyrazine, [Et8TPyzPAH2], in organic solvents (CH2Cl2, THF and DMSO) has revealed that it is easily deprotonated not only in the presence of strong bases such as tetrabutylammonium hydroxide, but also in such proton-acceptor solvent as DMSO. The thermodynamic acidity constants (pKa1 = 7.77 and pKa2 = 7.80) determined for [Et8TPyzPAH2] in DMSO solution using spectropotentiometric titration indicate that TPyzPA macrocycle has ∼ 1000 times stronger NH-acidity than phthalocyanine. Deprotonation of [Et8TPyzPAH2] in pyridine solution is only possible in the presence of water playing a crucial role in formation of the dianion, which can be considered as a sensitive spectral sensor for water traces. Theoretical DFT B3LYB/631++G(p,d) study has confirmed that the dianion is only stabilized as bisaqua complex [TPyzPA(H2O)2]2− with complementary H-bonds between water molecule and N-atoms of two opposite pyrrole rings (N…HOH…N).