3-hydroxypicolinic Acid Research Articles

Structural and Multi-functional properties of isoelectronic guanyl hydrazinium picolinic derivatives exhibit centric and non-centric space group

The equimolar reaction mixture of isoelectronic picolinic acid N-oxide (PAHNO) and/or 3-hydroxy picolinic acid (3-HPAH) with guanyl hydrazine bicarbonate (AgunH.HCO3) in aqueous medium at room temperature produce 1:1 salt. Irrespective of the molar ratios (1; 1, 1:2 & 2:1) and reaction conditions maintained, invariably gives the same product in the form of polycrystalline nature except 1:1 ratio which yields a single crystal. The isoelectronic salts were characterized by spectroscopic, PXRD, thermal study and single crystal X-ray diffraction techniques. In general, most of the salts were crystallized in a centric space group rather than a non-centric, the prevailing factors are nature of the organic species and reaction conditions like pH, pKa, solvent effects, temperature and molar ratio etc,. Surprisingly, in the present case, the isoelectric salt of [AgunH]+[PANO]- crystalized in centric (P21/n), where in case of [AgunH]+[3-HPA]- crystalized in non-centric (Pca21) space group even though in the same reaction conditions. This may be due to the presence of the 3rd position of hydroxyl group and non-covalent interactions in [AgunH]+[3-HPA]- that facilitate non-centric space group. Both salts are stabilized by the variety of hydrogen bond features leading to intra- and intermolecular N-H⋯O, N-H⋯N, and C-H⋯N hydrogen bonds and π-π stacking interactions along with homo- and hetero ring motifs [two R22 (8), R11 (6), and two R22 (9)]. These interactions render them an appropriate acid-base ion pair for the formation of sturdy hydrogen-bonded supramolecular synthons. Thermal studies on these salts reveal that the thermal degradation occurs via melting followed by complete loss of organic species. The solid-state emission spectra of free acids and its salts were recorded and compared. The materials exhibit a prominent luminescent character towards red shift than the starting compounds. Further, these materials show enhanced secondary antioxidant and antimicrobial activities, this is due to the crucial role of hydrazine species in guanyl hydrazinium cation.

Metabolic Profiling Reveals That the Olfactory Cues in the Duck Uropygial Gland Potentially Act as Sex Pheromones.

Simple SummaryFor birds, the uropygial gland is a special organ. We believe that its secretion can be used as a pheromone between the sexes to play a role in mate selection and mating. Therefore, we studied the chemical composition of duck uropygial gland secretions and the differences between males and females. After a series of screenings, 24 different volatile metabolites were obtained in our experiment. On this basis, five extremely significant volatile metabolites were screened out—significantly more males than females. The results show that these volatile substances are potential sex pheromone substances, which may be the critical olfactory clues for birds to choose mates. Our results lay the foundation for further research on whether uropygial gland secretion affects duck reproduction and production.The exchange of information between animals is crucial for maintaining social relations, individual survival, and reproduction, etc. The uropygial gland is a particular secretion gland found in birds. We speculated that uropygial gland secretions might act as a chemical signal responsible for sexual communication. We employed non-targeted metabolomic technology through liquid chromatography and mass spectrometry (LC-MS) to identifying duck uropygial gland secretions. We observed 11,311 and 14,321 chemical substances in the uropygial gland secretion for positive and negative ion modes, respectively. Based on their relative contents, principal component analysis (PCA) showed that gender significantly affects the metabolite composition of the duck uropygial gland. A total of 3831 and 4510 differential metabolites were further identified between the two sexes at the positive and negative ion modes, respectively. Of them, 139 differential metabolites were finally annotated. Among the 80 differential metabolites that reached an extremely significant difference (p < 0.01), we identified 24 volatile substances. Moreover, we further demonstrated that five kinds of volatile substances are highly repeatable in all testing ducks, including picolinic acid, 3-Hydroxypicolinic acid, indoleacetaldehyde, 3-hydroxymethylglutaric acid, and 3-methyl-2-oxovaleric acid. All these substances are significantly higher in males than in females, and their functions are involved in the reproduction processes of birds. Our data implied that these volatile substances act as sex pheromones and may be crucial olfactory clues for mate selection between birds. Our findings laid the foundation for future research on whether uropygial gland secretion can affect ducks’ reproduction and production.

Interaction of V(V) complexes formed by picolinic and pyrazinecarboxylic acid derivatives with red blood cells

The interaction with red blood cells (RBC) of vanadium(V) complexes formed by 3,5-difluoropicolinic acid (HpicFF), 3-hydroxypicolinic acid (H2hypic) and pyrazinecarboxylic acid (Hprz) has been examined. Electron Paramagnetic Resonance (EPR) spectroscopy results suggest that V(V) is reduced in all cases to V(IV) inside the erythrocytes. The thermodynamic stability of V(V) and corresponding V(IV) complexes has been related with the species detected in the cellular environment; when the ligands form unstable complexes with both VVO2+ and VIVO2+ ions (picFF and prz), the species formed inside RBC are similar to those observed when starting with vanadate(V) alone, that is VIVO2+ – formed upon V(V) reduction – which distributes among the cellular bioligands forming different types of complexes. When in the ligand molecule other groups able to form chelated complexes are present (H2hypic), more stable species are formed inside the RBC. The amount of complex able to enter the RBC depends on the ligand structure which could influence the metal uptake. The interaction of different VIVO2+ complexes formed by picolinate (picFF, pic = picolinate, picCN = 5-cyanopicolinate) and pyrazinecarboxylate (prz and przNH2 = 3-aminopyrazine-2-carboxylate) derivatives with hemoglobin (Hb), which is the main candidate to bind the VIVO2+ ion in the cytosol, was also investigated to rationalize the results. The ligands which form at physiological pH relatively stable complexes with VIVO2+ (przNH2 and pic) can give inside the erythrocytes mixed species after the replacement of an equatorial water molecule by an imidazole nitrogen of a histidine residue of the protein, while the ligands which form with VIVO2+ unstable complexes (picCN, picFF, prz) yield the same species observed in the binary system VIVO2+–Hb.

Ionic matrices for matrix-assisted laser desorption/ionization mass spectrometry analysis of microRNA biomarkers

The use of ionic matrices (IMs) was evaluated as an alternative to conventional matrices to analyze microRNAs (miRNAs) by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). 2, 4, 6-Trihydroxyacetophenone (THAP), 6-aza-2-thiothymine (ATT) and 3-hydroxypicolinic acid (3-HPA) and their IMs with pyridine (PYR) and butylamine (BA) were studied to analyze a standard mixture of miRNAs: miR-21, let-7g and iso-miR-16. Among all the studied matrices, ATT-PYR at 75 mg/mL in acetonitrile (MeCN):H2O (50:50, v/v) was selected as the optimal. Furthermore, addition of ammonium citrate dibasic (AC) as signal enhancer was mandatory to obtain an appropriate miRNA detection. ATT-PYR provided the best sensitivity, with limit of detection (LOD) up to 5 nM (equivalent to 1 fmol in the spot) and excellent spot-to-spot repeatability due to the improved homogeneity of the spots compared to the conventional matrices. The applicability of the established method to direct, multiplex and untargeted analysis of miRNAs in serum samples was also investigated.

Effect of matrices and additives on phosphorylated and ketodeoxyoctonic acid lipids A analysis by matrix-assisted laser desorption ionization-mass spectrometry.

Lipid A is a major compound of the outer membrane of gram-negative bacteria and is a key factor of bacterial virulence. As lipid A's structure differs among bacterial species and varies between strains of the same species, knowing its modifications is essential to understand its implications in the infectious process. To analyze these lipids, matrix-assisted laser desorption ionization-mass spectrometry (MALDI-MS) is a well-suited method that is fast and efficient. However, there are limitations with the matrix and additives used, such as the suppression of signal or prompt fragmentations that could give a false overview of lipid A composition in biological samples. For a comprehensive analysis of the entire lipid A species present in a sample, we tested 16 matrices and 11 additives on two commercial lipids A. The first commercial one contains single phosphorylation group, and the second contains two phosphorylation and two ketodeoxyoctonic acid (KDO) groups. The lipid A containing KDO groups was essentially detected by the 3-hydroxypicolinic acid (3-HPA) matrix, whereas the monophosphorylated lipid A could be detected by 13 matrices out of the 16. We also demonstrated that the signal of diphosphorylated lipid A can be enhanced with the use of additives in the matrix. Our study indicated that the best conditions to obtain a clear signal of both lipids A without prompt fragmentation was the use of 3-HPA with 10mM trifluoroacetic acid (TFA).

Gut Microbiota is the Key to the Antidepressant Effect of Chaihu-Shu-Gan-San.

Accumulating evidence highlights the link between gut microbiota and depression. As an antidepressant herbal drug in clinic, Chaihu-Shu-Gan-San (CSGS) has also been used in China for the treatment of various gastrointestinal disorders. Therefore, we hypothesize that the gut microbiota might be involved in the effect of CSGS. Here, we investigated the antidepressant effects of CSGS against chronic variable stress (CVS)-induced depression rats with and without antibiotic treatment using 16S rRNA gene sequencing and ultra-performance liquid chromatography coupled with time of flight mass spectrometry (UPLC-Q-TOF/MS) based metabolomics approaches. As a result, the prominent effects of CSGS against the depression-like behavioral disorder of CVS-induced rats were significantly weakened when the gut microbiota was changed after oral administration of the broad-spectrum antibiotic. The mediation of CSGS on hippocampal levels of serotonin (5-HT) and glutamic acid (Glu) was also receded with the antibiotic treatment. Further investigation on the diversity of microbiome indicated that the improvement effect of CSGS on gut microbiota dysbiosis—especially the phylum level of Firmicutes—was attenuated after the CSGS combined antibiotic treatment. Moreover, 3-hydroxypicolinic acid (H4) and inosine (H8) in the hippocampus were considered as important biomarkers for depression and are also associated with gut microbiota mediated CSGS efficacy. Taken together, our current study indicated that gut microbiota is a critical factor in the antidepressant effect of CSGS, which improve depression-related metabolic disturbance partly through gut microbiota.

In vitro reconstitution of the biosynthetic pathway of 3-hydroxypicolinic acid.

3-Hydroxypicolinic acid (3-HPA) is an important pyridine building block of bacterial secondary metabolites. Although the main biosynthetic pathways of these metabolites have been identified and well characterized, the enzymatic mechanism underlying the biosynthesis of 3-HPA has yet to be elucidated. In this work, we successfully reconstituted the complete biosynthetic pathway of 3-HPA in vitro. We showed that an l-lysine 2-aminotransferase, a two-component monooxygenase, and a FAD-dependent dehydrogenase are required to convert l-lysine to 3-HPA. We further demonstrated that 3-HPA does not derive from the direct hydroxylation of the picolinic acid at C-3, but from a successive process of C-3 hydroxylation of the piperideine-2-carboxylic acid and tautomerization of the produced 3-hydroxyl dihydropicolinic acid. Therefore, this study unveils the unusual assembly logic of 3-HPA and sheds light on the potential of engineering the 3-HPA pathway for generating novel pyridine-based building blocks.

Application of RT-PCR and MALDI-TOF MS for the detection of RNA luteovirus

There is a need for rapid and less expensive methods to identify RNA viruses, including luteoviruses, for practical use in agriculture and quarantine. The mass spectrometric cleaved amplified polymorphic sequence (MS-CAPS) method, which detects enzymatically cleaved amplicons by matrix-assisted laser desorption/ionization mass spectrometry, was herein used together with a short RT-PCR to detect luteovirus in only 90 min. In addition, the matrixes 2′,4′,6′-trihydroxyacetophene and 3-hydroxypicolinic acid were compared for their effectiveness in the analysis of short single-stranded biotinylated DNA obtained by a MS-CAPS reaction.

Comprehension of the Effect of a Hydroxyl Group in Ancillary Ligand on Phosphorescent Property for Heteroleptic Ir(III) Complexes: A Computational Study Using Quantitative Prediction.

A new Ir(III) complex (dfpypya)2Ir(pic-OH) (2) is theoretically designed by introduction of a simple hydroxyl group into the ancillary ligand on the basis of (dfpypya)2Ir(pic) (1) with the aim to get the high-efficiency and stable blue-emitting phosphors, where dfpypya is 3-methyl-6-(2',4'-difluoro-pyridinato)pyridazine, pic is picolinate, and pic-OH is 3-hydroxypicolinic acid. The other configuration (dfpypya)2Ir(pic-OH)' (3) is also investigated to compare with 2. The difference between 2 and 3 is whether the intramolecular hydrogen bond is formed in the (dfpypya)2Ir(pic-OH). The quantum yield is determined by three different methods including the semiquantitative and quantitative methods. To quantitatively determine the quantum yield is still not an easy task to be completed. This work would provide some useful advices to select the suitable method to reliably evaluate the quantum yield. Complex 2 has larger quantum yield and more stability as compared with 1 and 3. The formation of intramolecular hydrogen bond would become a new method to design new phosphor with the desired properties.

New Insights into the Wavelength Dependence of MALDI Mass Spectrometry.

The interplay between the wavelength of the laser and the absorption profile of the matrix constitutes a crucial factor in matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS). Numerous studies have shown that typically best analytical results are obtained if the laser wavelength matches the UV absorption band of the matrix in the solid state well. However, many powerful matrices exhibit peak absorptions which differ notably from the standard MALDI laser wavelengths of 337, 349, and 355 nm, respectively. Here we used two wavelength-tunable lasers to investigate the MALDI wavelength dependence with a selected set of such matrices. We studied 3-hydroxypicolinic acid (3-HPA), 2,4,6-trihydroxyacetophenon (THAP), dithranol (1,8-dihydroxy-10H-anthracen-9-on), 2-(4'-hydroxybenzeneazo)benzoic acid (HABA), and 6-aza-2-thiothymine (ATT). For analyte systems we investigated DNA oligomers (3-HPA), phospholipids (dithranol, THAP, HABA), and non-covalent peptide-peptide and protein-peptide complexes (ATT). We recorded analyte ion and total ion counts as a function of wavelength and laser fluence between 213 and 600 nm. Although the so-generated comprehensive heat maps generally corroborated the previously made findings, several fine features became notable. For example, despite a still high optical absorption exhibited by some of the matrices in the visible wavelength range, ion yields generally dropped strongly, indicating a change in ionization mechanism. Moreover, the non-covalent complexes were optimally detected at wavelengths corresponding to a relatively low optical absorptivity of the ATT matrix, presumably because of ejection of a particular cold MALDI plume. Our comprehensive data shed useful light into the MALDI mechanisms and could assist in further methodological advancement of the technique.

Synthesis, cytotoxic and antitubercular activities of copper(II) complexes with heterocyclic bases and 3-hydroxypicolinic acid

Two new copper(II) complexes with the deprotonated ligand 3-hydroxypicolinic acid (3-HPA) and heterocyclic bases (1,10-phenanthroline – phen or 2,2′-bipyridine – bpy) were synthesized. [Cu(3-HPA)(phen)ClO4] I and [Cu(3-HPA)(bpy)ClO4] II were characterized by elemental analyses, conductivity measurements, FT-IR, UV–Vis, EPR and High-resolution Electrospray Ionization Mass Spectrometry (HRESIMS). The results indicate that the geometry around the copper ion is distorted square-pyramidal, and that the copper ion is coordinated to 3-HPA via oxygen and nitrogen atoms, and to heterocyclic bases via their two nitrogen atoms. A perchlorate ion weakly bonded occupies the apical position, completing the metal coordination sphere. In this work, the compound [Cu(3-HPA)2] III was also synthesized using a new method, different from that described in the literature. The cytotoxic activity of these compounds against tumor and normal cell lines was investigated. Complex I exhibited a strong antitumor activity, being the most active in the series of studied complexes. The compounds were also evaluated for activity against Mycobacterium tuberculosis, and the complex I displays good antimycobacterial activity, while compounds II and III were only moderately active.

Characterization of the Biosynthetic Gene Cluster for Benzoxazole Antibiotics A33853 Reveals Unusual Assembly Logic

A33853, which shows excellent bioactivity against Leishmania, is a benzoxazole-family compound formed from two moieties of 3-hydroxyanthranilic acid and one 3-hydroxypicolinic acid. In this study, we have identified the gene cluster responsible for the biosynthesis of A33853 in Streptomyces sp. NRRL12068 through genome mining and heterologous expression. Bioinformatics analysis and functional characterization of the orfs contained in the gene cluster revealed that the biosynthesis of A33853 is directed by a group of unusual enzymes. In particular, BomK, annotated as a ketosynthase, was found to catalyze the amide bond formation between 3-hydroxypicolinic and 3-hydroxyanthranilic acid during the assembly of A33853. BomJ, a putative ATP-dependent coenzyme A ligase, and BomN, a putative amidohydrolase, were further proposed to be involved in the benzoxazole formation in A33853 according to gene deletion experiments. Finally, we have successfully utilized mutasynthesis to generate two analogs of A33853, which were reported previously to possess excellent anti-leishmanial activity.

Ruthenium(II) complexes with hydroxypyridinecarboxylates: Screening potential metallodrugs against Mycobacterium tuberculosis

Three promising antimycobacterium tuberculosis ruthenium(II) complexes with the deprotonated ligands 2-hydroxynicotinic acid (2-OHnicH), 6-hydroxynicotinic acid (6-OHnicH) and 3-hydroxypicolinic acid (3-OHpicH) were synthesized and characterized. Structural analysis revealed three different coordination modes depending of the hydroxypyridinecarboxylate ligand. In the complex [Ru(2-OHnic)(dppb)(bipy)]PF6 (1), the 2-OHnic anion is coordinated by the O,O-chelating mode (via carboxylate group and phenolate oxygen), in the [Ru(6-OHnic)(dppb)(bipy)]PF6 (2) a O–O chelation by the carboxylate group is observed for the 6-OHnic ligand and for the complex [Ru(3-OHpic)(dppb)(bipy)]PF6 (3) a N,O-chelating mode (via carboxylate) occurs to the 3-OHpic anion. The compounds were evaluated for activity against Mycobacterium tuberculosis H37Rv ATCC 27294 using Resazurin Microtitre Assay (REMA) plate method and cytotoxicity in VERO CCL-81 cell line. All the synthesized compounds exhibited good antimycobacterial activity and a completely lack of cytotoxicity activity, indicating a good selectivity index.

Is energy pooling necessary in ultraviolet matrix‐assisted laser desorption/ionization?

Energy pooling has been suggested as the key process for generating the primary ions during ultraviolet matrix-assisted laser desorption/ionization (UV-MALDI). In previous studies, decreases in fluorescence quantum yields as laser fluence increased for 2-aminobenzoic acid, 2,5-dihydroxybenzoic acid (2,5-DHB), and 3-hydroxypicolinic acid were used as evidence of energy pooling. This work extends the research to other matrices and addresses whether energy pooling is a universal property in UV-MALDI. Energy pooling was investigated in a time-resolved fluorescence experiment by using a short laser pulse (355 nm, 20 ps pulse width) for excitation and a streak camera (1 ps time resolution) for fluorescence detection. The excited-state lifetime of 2,5-DHB decreased with increases in laser fluence. This suggests that a reaction occurs between two excited molecules, and that energy pooling may be one of the possible reactions. However, the excited-state lifetime of 2,4,6-trihydroxyacetophenone (THAP) did not change with increases in laser fluence. The upper limit of the energy pooling rate constant for THAP is estimated to be approximately 100-500 times smaller than that of 2,5-DHB. The small energy pooling rate constant for THAP indicates that the potential contribution of the energy pooling mechanism to the generation of THAP matrix primary ions should be reconsidered.

Heteronuclear phosphorescent iridium(iii) complexes with tunable photophysical and excited-state properties by chelating BF2 moiety for application in bioimaging

In the present study, we explored a novel design strategy of heteronuclear phosphorescent iridium(III) complexes chelated by BF2 moiety with 3-hydroxypicolinic acid as the chelate ligand and synthesized a new series of iridium(III) complexes [Ir(dfppy)2(hpa)BF2] (1b), [Ir(ppy)2(hpa)BF2] (2b) and [Ir(tpq)2(hpa)BF2] (3b) (hpa = 3-hydroxypicolinic acid, dfppy = 2-(2,4-difluorophenyl)pyridine, ppy = 2-phenylpyridine, tpq = 2-(thiophen-2-yl)quinoline) under mild conditions. The emission colors and wavelengths of iridium(III) complexes can be affected evidently by chelating BF2 moiety into iridium(III) complexes, and this effect will be changed with the difference of cyclometalating CˆN ligands. A combination of UV-vis absorption, photoluminescence, excited-state lifetime measurements and theoretical calculations has provided the significant insight into the nature of the excited state and photophysical properties of these interesting iridium(III) complexes. Moreover, the exclusive staining of cytoplasm and low cytotoxicity were demonstrated for these new iridium(III) complexes, which made them promising candidates as multi-color phosphorescent dyes for living cell imaging.

Functionalization of Monodisperse Iron Oxide NPs and Their Properties as Magnetically Recoverable Catalysts

Here we report the functionalization of monodisperse iron oxide nanoparticles (NPs) with commercially available functional acids containing multiple double bonds such as linolenic (LLA) and linoleic (LEA) acids or pyridine moieties such as 6-methylpyridine-2-carboxylic acid, isonicotinic acid, 3-hydroxypicolinic acid, and 6-(1-piperidinyl)pyridine-3-carboxlic acid (PPCA). Both double bonds and pyridine groups can be reacted with noble metal compounds to form catalytically active species in the exterior of magnetic NPs, thus making them promising magnetically recoverable catalysts. We determined that both LLA and LEA stabilize magnetic iron oxide NPs, allowing the formation of π-complexes with bis(acetonitrile)dichloropalladium(II) in the NP shells. In both cases, this leads to the formation of NP aggregates because of interparticle complexation. In the case of pyridine-containing ligands, only PPCA with two N-containing rings is able to provide NP stabilization and functionalization whereas other pyridine-containing acids did now allow sufficient steric stabilization. The interaction of PPCA-based particles with Pd acetate also leads to aggregation because of interparticle interactions, but the aggregates that are formed are much smaller. Nevertheless, the catalytic properties in the selective hydrogenation of dimethylethynylcarbinol (DMEC) to dimethylvinylcarbinol were the best for the catalyst based on LLA, demonstrating that the NP aggregates in all cases are penetrable for DMEC. Easy magnetic separation of this catalyst from the reaction solution makes it promising as a magnetically recoverable catalyst.

Oligonucleotide Models of Telomeric DNA and RNA Form a Hybrid G-quadruplex Structure as a Potential Component of Telomeres

Telomeric repeat-containing RNA, a non-coding RNA molecule, has recently been found in mammalian cells. The detailed structural features and functions of the telomeric RNA at human chromosome ends remain unclear, although this RNA molecule may be a key component of the telomere machinery. In this study, using model human telomeric DNA and RNA sequences, we demonstrated that human telomeric RNA and DNA oligonucleotides form a DNA-RNA G-quadruplex. We next employed chemistry-based oligonucleotide probes to mimic the naturally formed telomeric DNA-RNA G-quadruplexes in living cells, suggesting that the process of DNA-RNA G-quadruplex formation with oligonucleotide models of telomeric DNA and RNA could occur in cells. Furthermore, we investigated the possible roles of this DNA-RNA G-quadruplex. The formation of the DNA-RNA G-quadruplex causes a significant increase in the clonogenic capacity of cells and has an effect on inhibition of cellular senescence. Here, we have used a model system to provide evidence about the formation of G-quadruplex structures involving telomeric DNA and RNA sequences that have the potential to provide a protective capping structure for telomere ends.

Vibrational spectroscopic and DFT calculation studies of cobalt(II) complexes with 3-hydroxypicolinic acid

Two cobalt(II) complexes with 3-hydroxypicolinic acid (3-hydroxypyridine-2-carboxylic acid, 3-OHpicH), trans-[Co(3-OHpic)2(py)2] (2) and cis-[Co(3-OHpic)2(4-pic)2] (3) (py=pyridine; 4-pic=4-picoline or 4-methylpyridine), previously synthesized and characterized by X-ray diffraction, are here studied by Raman and mid-infrared spectroscopy with the help from the corresponding DFT vibrational calculations using B3LYP/6-311G(d,p) computational model. Intramolecular O–H⋯O hydrogen bond appears in both complexes 2 and 3, while weak C–H⋯O hydrogen bonds assemble molecules of 2 or 3 into 3D architecture. A complete presentation of all Raman, infrared and theoretical results is given for complex 3. The measured spectra are shown, relative intensities and bandwidths are discussed and the assignment of vibrational bands is given on the basis of the DFT calculations. The calculated spectra agree very well with the presented experimental findings, thanks to the suitable grouping of modes. The same vibrational calculations also reveal insignificant influence of H→CH3 substitution for the spectroscopic characterization of the complex. A careful study of differences between calculated and observed wavenumbers suggests that modified single-factor scaling is actually better than the classic multi-factor scaling approach.

Two new metal-organic coordination polymers of lead with O-, N-donor ligands: Synthesis, characterization, luminescence and thermal behavior

The synthesis of two new lead(II) coordination polymers, [Pb2(picOH)4]·H2O (1) and [Pb3(Sip)2(H2O)2]·H2O (2) has been reported, where HpicOH=3-hydroxypicolinic acid and NaH2Sip=5-sulfoisophthalic acid monosodium salt. Both the complexes were structurally characterized by X-ray single crystal diffraction analysis. Complex 1, where the 3-hydroxypicolinate ligand is used for the first time in conjunction with Pb(II), revealed to be a 1D polymeric array. Complex 2 showed a 3D structure with 5-sulfoisophthalate ligand adopting two novel binding modes of high denticity (η6μ6 and η7μ7). The photoluminescence and thermal properties of the two complexes have been studied.

Structural preferences and isomerism in nickel(II) and copper(II) complexes with 3-hydroxypicolinic acid

Recrystallization of [Ni(3-OHpic)2(H2O)2] (1) from pyridine (py) affords trans-[Ni(3-OHpic)2(py)2] (2), while cis-[Ni(3-OHpic)2(4-pic)2] (3) is obtained from 4-picoline (4-pic). The nickel(II) ion is octahedrally coordinated by two N,O-bidentate 3-hydroxypicolinate ligands in both 2 and 3, and by two pyridine molecules in trans positions (2) or two 4-picoline molecules in cis positions (3). [Cu(3-OHpic)2] reacted with 4-picoline to yield the pentacoordinated species [Cu(3-OHpic)2(4-pic)] (4), but in the presence of 3-picoline (3-pic) the octahedral trans-[Cu(3-OHpic)2(3-pic)2] (5), similar to 2, was isolated. The crystal structures of 2–5 exhibit strong intramolecular O–H···O hydrogen bonds, but the intermolecular interactions are weak (C–H···O hydrogen bonds, π–π and C–H···π interactions). DFT calculations showed a preference for octahedral coordination for both the nickel(II) and copper(II) complexes, and a very small preference for a cis arrangement of the monodentate ligands, as observed in 2 and 5. The cooperative effect of weak intermolecular interactions should be responsible for reversing the preferences, but no major driving force could be identified. Calculated (DFT) and experimental IR spectra for 2–5 were compared and characteristic bands assigned. Thermogravimetric studies showed the initial loss of two coordinated pyridine, 4-picoline or 3-picoline molecules in 2, 3 and 5, respectively.