1,721,110 research outputs found
Co-crystallisation of cytosine with 1,10-phenanthroline: computational screening and experimental realisation
No full textAttempts to co-crystallise the nucleobases adenine, thymine, guanine, and cytosine with 1,10-phenanthroline by ball milling and solvent evaporation methods are described. A 1 : 1 co-crystal of cytosine and 1,10-phenanthroline can be obtained by grinding or by solvent evaporation. The structure contains two crystallographically independent cytosine and two independent 1,10-phenanthroline molecules (Z? = 2). The cytosine molecules form two similar but crystallographically independent hydrogen-bonded chains, while the 1,10-phenanthroline molecules are arranged in ?-stacks. Between the chains of cytosine and the ?-stacks exist N–H?N and C–H?N interactions. Crystal structure prediction (CSP) calculations were applied to all four systems to assess their potential for co-crystallisation as well as the likely structures and intermolecular interactions that could result from co-crystallisation. Calculations on the cytosine system demonstrate that co-crystallisation results in a lower energy than the crystalline forms of the two starting materials, in line with the co-crystal formation observed. For the systems which did not form a co-crystal, CSP was used to explore potential packing arrangements, but found none which were lower in energy than that of the pure crystalline forms. In these cases there is significant disruption to the nucleobase hydrogen bonding between the pure compound and the hypothetical co-crystal. For pure adenine and guanine, the hydrogen-bonded ribbons form sheets which must be broken, whereas for thymine, the lack of hydrogen bond donors does not allow the hydrogen bonding present for pure thymine to be maintained while forming thymine-1,10-phenanthroline hydrogen bonds
Structural diversity in imidazolidinone organocatalysts: a synchrotron and computational study
No full text(S)-1-(Methylaminocarbonyl)-3-phenylpropanaminium chloride (S2·HCl), C10H15N2O+·Cl-, crystallizes in the orthorhombic space group P212121 with a single formula unit per asymmetric unit. (5R/S)-5-Benzyl-2,2,3-trimethyl-4-oxoimidazolidin-1-ium chloride (R3 and S3), C13H19N2O+·Cl-, crystallize in the same space group as S2·HCl but contain three symmetry-independent formula units. (R/S)-5-Benzyl-2,2,3-trimethyl-4-oxoimidazolidin-1-ium chloride monohydrate (R4 and S4), C13H19N2O+·Cl-·H2O, crystallize in the space group P21 with a single formula unit per asymmetric unit. Calculations at the B3LYP/6-31G(d,p) and B3LYP/6-311G(d,p) levels of the conformational energies of the cation in R3, S3, R4 and S4 indicate that the ideal gas-phase global energy minimum conformation is not observed in the solid state. Rather, the effects of hydrogen-bonding and van der Waals interactions in the crystal structure cause the molecules to adopt higher-energy conformations, which correspond to local minima in the molecular potential energy surface.<br/
Synthesis, characterisation and ROP catalytic evaluation of Cu(II) complexes bearing 2,2ʹ-diphenylglycine-derived moieties
Full text linkThe treatment of CuX2 (X = Cl, Br) with an equimolar amount of 2-2ʹ-diphenylglycine (DpgH) in EtOH at reflux afforded, after work up, the complexes [CuCl(Dpg)(EtOH)]2 (1) and [(CuBr2)2(Dpg)2Cu(EtOH)4] (2), respectively. The compounds were obtained microanalytically pure in low to moderate yield (13 and 27%, respectively) and were fully characterised. Synthetic attempts towards Cu-alkoxide species led to the isolation of the heterobimetallic species [(CuCl2)(Dpg)Li(THF)]·THF (3·THF). Finally, complex 4, bearing an imine ligand derived from the decarboxylation of DpgH, was serendipitously obtained from the synthesis of 3. These complexes were found to be inactive in the homo- and co-ring opening polymerization (ROP) of cyclic esters (ε-caprolactone and rac-lactide) and epoxides (propylene oxide and cyclohexene oxide). Compounds 1 and 2 were shown to be non-toxic against cancerous cell lines HCT116 and HT-29
Ring Opening Polymerization of Lactides and Lactones by Multimetallic Titanium Complexes Derived from the Acids Ph2C(X)CO2H (X = OH, NH2)
Full text linkThe reactions of the titanium alkoxide [Ti(OR)4] (R = Me, nPr, iPr, tBu) with the acids 2,2’-Ph2C(X)(CO2H), where X = OH and NH2, i.e., benzilic acid (2,2’-diphenylglycolic acid, L1H2), and 2,2’-diphenylglycine (L2H3), have been investigated. The variation of the reaction stoichiometry allows for the isolation of mono-, bi-, tri or tetra-metallic products, the structures of which have been determined by X-ray crystallography. The ability of the resulting complexes to act as catalysts for the ring opening polymerization (ROP) of ε-caprolactone (ε-CL) and r-lactide (r-LA) has been investigated. In the case of ε-CL, all catalysts except that derived from [Ti(OnPr)4] and L2H3, i.e., 7, exhibited an induction period of between 60 and 285 min, with 7 exhibiting the best performance (>99% conversion within 6 min). The PCL products are moderate- to high-molecular weight polymers. For r-LA, systems 1, 3, 4 and 7 afforded conversions of ca. 90% or more, with 4 exhibiting the fastest kinetics. The molecular weights for the PLA are somewhat higher than those of the PCL, with both cyclic and linear PLA products (end groups of OR/OH) identified. Comparative studies versus the [Ti(OR)4] starting materials were conducted, and although high conversions were achieved, the control was poor
Novel copper coordination compounds of amino acids and pyridines : synthesis, characterisation, physical properties, and future prospects for gas adsorption
No full textThe primary goal of the work discussed in this thesis was to assess the capability of cheap, readily available ligands, e.g. pyridines and amines, to produce new coordination compounds, primarily with copper, that could lead to the development of novel materials for gas adsorption. Chapters 1 and 2 introduce the topic and methods respectively, results are contained within chapters 3-6.Chapter 3 describes the synthesis, polymorphism and solid-gas reactions of [CuCl₂(RPy)₂] and (RPy-H)[CuCl₄] (RPy: R = 4-CO₂H, 4-CONH₂, 3-CONH₂). The polymeric [CuCl₂(RPy)₂] compounds appear blue, while the equivalent (RPy-H)[CuCl₄] salts appear yellow or green depending on the geometry of the [CuCl₄]²⁻ ion. Exchange between the two types of compound is possible through the gain and loss of HCl, although the exact mechanism and what causes the observed differences in reaction is uncertain. [CuCl₂(RPy)₂] compounds could be developed further into porous materials through the use of simple tris(pyridine) ligands.Chapter 4 discusses a facile synthetic method for [Cu₄(μ⁴-O)(μ²-Cl)6(RPy)₄] compounds via the oxidation of CuCl in the presence of [CuCl₂(RPy)₂]n (RPy: R = 4-Me, 4-NH₂, 4-NMe₂). The production of the [Cu₄(μ⁴-O)(μ²-Cl)6(RPy)₄] cluster only seems to occur for compounds where the [CuCl₂(RPy)₂] complex is non-polymeric or at least weakly polymeric. Only one porous [Cu₄(μ⁴-O)(μ²-Cl)6(RPy)₄] compound is known with 1,4-diazabicyclo[2.2.2]octane, but there is potential for others to be discovered. However, these compounds are not as stable as other compounds that might be used for gas adsorption and are better suited for catalysis applications.Chapter 5 focuses on the copper and zinc coordination chemistry of amino acids with general formula CO₂H-(CH₂)n-NH₂ (where n = 1-5 and 7). Amino acids are a good potential ligand for CO₂ capture given their similarity with monoethanolamine: the most common chemical used in industrial technologies. However, their flexibility and propensity to form zwitterions means that the majority of compounds produced were adducts of copper halides, and those which were not appeared too dense for application in CO₂ adsorption. The copper halide adducts showed similar HCl/HBr gas uptake as the [CuCl₂(RPy)₂] compounds in chapter 3, although the reverse reaction was much slower with very little change observed over several months.Lastly, chapter 6 details the novel coordination compounds created using Cu and a combination of various benzoic acid based and pyridine-based ligands. Most of the novel compounds have only been structurally characterised and no general conclusions can be made about their structures due to the lack of data. One compound made with 4-hydroxybenzoic acid and pyrazine in methanol showed promise for methanol adsorption, however the compound could not be made reliably or quantities large enough to study the phenomenon further
DNA bases in crystal engineering
Full text linkThe work described in this thesis focuses on understanding the solid state interactions of organic molecules such as DNA nucleobases using established principles from crystal engineering and the synthon theory. Studying the intermolecular interactions is an indispensable tool to the crystal engineer when it comes to identifying functional groups which generate synthons that govern molecular recognition and self-assembly.Chapter 3 focuses on the growth and design of single crystal materials of DNA bases and their carboxylic acid derivatives with various other molecules. The aim of the chapter was to probe the hydrogen bonding displayed by these systems. The challenges associated with dissolving the nucleobases in organic and aqueous solvents prompted alternative synthetic route to mitigate solubility challenges. Altering the pH of the system was found useful in aiding dissolution. Such synthetic approach has led to the preparation of novel nucleobase salts of bis-guaninium sulphate in three different hydrate forms. The material obtained was a channel hydrate and it was possible to remove water partially and fully while retaining crystallinity. No structural collapse was observed upon full dehydration and the material obtained contained an empty channel hydrate. Co-crystallisation of cytosine with 1,10-phenanthroline is discussed in depth and the results are compared to crystal structure prediction results to rationalise co-crystal formation from an energetic perspective. Calculations on the energy landscape revealed that in the case of cytosine and 1,10-phenanthroline there is a favourable energetic driving force for co-crystallisation. This, however, does not apply to the co-crystallisation of the other DNA bases with 1,10-phenanthroline as these systems did not produce co-crystals and remained as mixtures of precursors. The chapter also describes structural features of thymine acetic acid, melaminium nitrilotriacetate trihydrate and co-crystals of caffeine with 2-nitroterepthalic acid. These structures are closely examined for their hydrogen bonding motifs.Chapter 4 covers a wide range of coordination compounds which relate to hydrogen-bonded networks of DNA nucleobases and their carboxylic acid derivatives. These complex architectures contain both coordination bonds as well as intermolecular interactions in the form of hydrogen bonding and stacking interactions. Metal-dipicolinate complexes treated with adenine and cytosine afforded hydrogen-bonded networks where protonated DNA bases interacted with the ligand via hydrogen bonding. The chapter discusses the role of water molecules in acting as spacers and stabilising crystal structure, especially in cases where there is an imbalance of hydrogen bond donors and acceptors.Orotic acid was heavily used owing to its chelating nature. This part of Chapter 4 focuses on novel crystal structures where orotic acid utilises its hydrogen bonding capability. An extensive discussion is provided on how the level of hydration impacts crystal packing and alters synthon formation. In addition, the chapter also focuses on the structural changes resulting from changing the position of the functional group in the ligand
Novel copper coordination compounds of amino acids and pyridines : synthesis, characterisation, physical properties, and future prospects for gas adsorption
Full text linkThe primary goal of the work discussed in this thesis was to assess the capability of cheap, readily available ligands, e.g. pyridines and amines, to produce new coordination compounds, primarily with copper, that could lead to the development of novel materials for gas adsorption. Chapters 1 and 2 introduce the topic and methods respectively, results are contained within chapters 3-6.Chapter 3 describes the synthesis, polymorphism and solid-gas reactions of [CuCl₂(RPy)₂] and (RPy-H)[CuCl₄] (RPy: R = 4-CO₂H, 4-CONH₂, 3-CONH₂). The polymeric [CuCl₂(RPy)₂] compounds appear blue, while the equivalent (RPy-H)[CuCl₄] salts appear yellow or green depending on the geometry of the [CuCl₄]²⁻ ion. Exchange between the two types of compound is possible through the gain and loss of HCl, although the exact mechanism and what causes the observed differences in reaction is uncertain. [CuCl₂(RPy)₂] compounds could be developed further into porous materials through the use of simple tris(pyridine) ligands.Chapter 4 discusses a facile synthetic method for [Cu₄(μ⁴-O)(μ²-Cl)6(RPy)₄] compounds via the oxidation of CuCl in the presence of [CuCl₂(RPy)₂]n (RPy: R = 4-Me, 4-NH₂, 4-NMe₂). The production of the [Cu₄(μ⁴-O)(μ²-Cl)6(RPy)₄] cluster only seems to occur for compounds where the [CuCl₂(RPy)₂] complex is non-polymeric or at least weakly polymeric. Only one porous [Cu₄(μ⁴-O)(μ²-Cl)6(RPy)₄] compound is known with 1,4-diazabicyclo[2.2.2]octane, but there is potential for others to be discovered. However, these compounds are not as stable as other compounds that might be used for gas adsorption and are better suited for catalysis applications.Chapter 5 focuses on the copper and zinc coordination chemistry of amino acids with general formula CO₂H-(CH₂)n-NH₂ (where n = 1-5 and 7). Amino acids are a good potential ligand for CO₂ capture given their similarity with monoethanolamine: the most common chemical used in industrial technologies. However, their flexibility and propensity to form zwitterions means that the majority of compounds produced were adducts of copper halides, and those which were not appeared too dense for application in CO₂ adsorption. The copper halide adducts showed similar HCl/HBr gas uptake as the [CuCl₂(RPy)₂] compounds in chapter 3, although the reverse reaction was much slower with very little change observed over several months.Lastly, chapter 6 details the novel coordination compounds created using Cu and a combination of various benzoic acid based and pyridine-based ligands. Most of the novel compounds have only been structurally characterised and no general conclusions can be made about their structures due to the lack of data. One compound made with 4-hydroxybenzoic acid and pyrazine in methanol showed promise for methanol adsorption, however the compound could not be made reliably or quantities large enough to study the phenomenon further
DNA bases in crystal engineering
Full text linkThe work described in this thesis focuses on understanding the solid state interactions of organic molecules such as DNA nucleobases using established principles from crystal engineering and the synthon theory. Studying the intermolecular interactions is an indispensable tool to the crystal engineer when it comes to identifying functional groups which generate synthons that govern molecular recognition and self-assembly.Chapter 3 focuses on the growth and design of single crystal materials of DNA bases and their carboxylic acid derivatives with various other molecules. The aim of the chapter was to probe the hydrogen bonding displayed by these systems. The challenges associated with dissolving the nucleobases in organic and aqueous solvents prompted alternative synthetic route to mitigate solubility challenges. Altering the pH of the system was found useful in aiding dissolution. Such synthetic approach has led to the preparation of novel nucleobase salts of bis-guaninium sulphate in three different hydrate forms. The material obtained was a channel hydrate and it was possible to remove water partially and fully while retaining crystallinity. No structural collapse was observed upon full dehydration and the material obtained contained an empty channel hydrate. Co-crystallisation of cytosine with 1,10-phenanthroline is discussed in depth and the results are compared to crystal structure prediction results to rationalise co-crystal formation from an energetic perspective. Calculations on the energy landscape revealed that in the case of cytosine and 1,10-phenanthroline there is a favourable energetic driving force for co-crystallisation. This, however, does not apply to the co-crystallisation of the other DNA bases with 1,10-phenanthroline as these systems did not produce co-crystals and remained as mixtures of precursors. The chapter also describes structural features of thymine acetic acid, melaminium nitrilotriacetate trihydrate and co-crystals of caffeine with 2-nitroterepthalic acid. These structures are closely examined for their hydrogen bonding motifs.Chapter 4 covers a wide range of coordination compounds which relate to hydrogen-bonded networks of DNA nucleobases and their carboxylic acid derivatives. These complex architectures contain both coordination bonds as well as intermolecular interactions in the form of hydrogen bonding and stacking interactions. Metal-dipicolinate complexes treated with adenine and cytosine afforded hydrogen-bonded networks where protonated DNA bases interacted with the ligand via hydrogen bonding. The chapter discusses the role of water molecules in acting as spacers and stabilising crystal structure, especially in cases where there is an imbalance of hydrogen bond donors and acceptors.Orotic acid was heavily used owing to its chelating nature. This part of Chapter 4 focuses on novel crystal structures where orotic acid utilises its hydrogen bonding capability. An extensive discussion is provided on how the level of hydration impacts crystal packing and alters synthon formation. In addition, the chapter also focuses on the structural changes resulting from changing the position of the functional group in the ligand
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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