The effect of amino acid backbone length on molecular packing: crystalline tartrates of glycine, β‐alanine, γ‐aminobutyric acid (GABA) and dl‐α‐aminobutyric acid (AABA)

We report a novel 1:1 cocrystal of β‐alanine with dl ‐tartaric acid, C₃H₇NO₂·C₄H₆O₆, (II), and three new molecular salts of dl ‐tartaric acid with β‐alanine {3‐azaniumylpropanoic acid–3‐azaniumylpropanoate dl ‐tartaric acid–dl ‐tartrate, [H(C₃H₇NO₂)₂]⁺·[H(C₄H₅O₆)₂]⁻, (III)}, γ‐aminobutyric acid [3‐carboxypropanaminium dl ‐tartrate, C₄H₁₀NO₂⁺·C₄H₅O₆⁻, (IV)] and dl ‐α‐aminobutyric acid {dl ‐2‐azaniumylbutanoic acid–dl ‐2‐azaniumylbutanoate dl ‐tartaric acid–dl ‐tartrate, [H(C₄H₉NO₂)₂]⁺·[H(C₄H₅O₆)₂]⁻, (V)}. The crystal structures of binary crystals of dl ‐tartaric acid with glycine, (I), β‐alanine, (II) and (III), GABA, (IV), and dl ‐AABA, (V), have similar molecular packing and crystallographic motifs. The shortest amino acid (i.e. glycine) forms a cocrystal, (I), with dl ‐tartaric acid, whereas the larger amino acids form molecular salts, viz. (IV) and (V). β‐Alanine is the only amino acid capable of forming both a cocrystal [i.e. (II)] and a molecular salt [i.e. (III)] with dl ‐tartaric acid. The cocrystals of glycine and β‐alanine with dl ‐tartaric acid, i.e. (I) and (II), respectively, contain chains of amino acid zwitterions, similar to the structure of pure glycine. In the structures of the molecular salts of amino acids, the amino acid cations form isolated dimers [of β‐alanine in (III), GABA in (IV) and dl ‐AABA in (V)], which are linked by strong O—H…O hydrogen bonds. Moreover, the three crystal structures comprise different types of dimeric cations, i.e. (A…A)⁺ in (III) and (V), and A⁺…A⁺ in (IV). Molecular salts (IV) and (V) are the first examples of molecular salts of GABA and dl ‐AABA that contain dimers of amino acid cations. The geometry of each investigated amino acid (except dl ‐AABA) correlates with the melting point of its mixed crystal.     

Lanthanide(III) nitrobenzenesulfonates and p-toluenesulfonate complexes of lanthanide(III), iron(III), and copper(II) as novel catalysts for the formation of calix[4]resorcinarene

Lanthanide(III) salts of p-toluenesulfonic acid [lanthanide(III) tosylates, Ln(TOS)₃] and nitrobenzenesulfonic acid [Ln(NBSA)₃], and p-toluenesulfonate complexes of iron(III) and copper(II) were prepared, characterized, and examined as catalysts for the synthesis of resorcinol-derived calix[4]resorcinarenes. The reaction of resorcinol with benzaldehyde yields two isomers, the all-cis isomer (rccc) and the cis-trans-trans isomer (rctt) with the relative isomer ratios depending on the reaction conditions. However, in the reaction of resorcinol with octanal only one isomer, the all-cis isomer, is formed in high yields with less than 0.1 mol % of Yb(TOS)₃. Examination of lanthanide(III) tosylates and lanthanide(III) nitrobenzenesulfonates revealed that ytterbium(III) 4-nitrobenzenesulfonate [ytterbium(III) nosylate, Yb(4-NBSA)₃] and ytterbium(III) 2,4-dinitrobenzenesulfonate [Yb(2,4-NBSA)₃] are the most active catalysts. The catalysts could be easily recovered and reused several times for resorcinarene formation without loss of efficiency. Surprisingly good results were also obtained with iron(III) and copper(II) p-toluenesulfonates. Besides optimizing the reaction conditions, new insights into the reaction mechanism were also obtained.     

OPTICALLY ACTIVE BIS(BIQUANIDE)COBALT(III) COMPLEXES CONTAINING AMINO ACIDS

Abstract

Biguanide-amino acid complexes of the type Co(am)(Hbg)³⁺ ₂, where am is the anion of glycine, sarcosine, L-alanine, L-valine, L-isoleucine, or L-proline, have been prepared and resolved. The absorption, circular dichroism (CD) and proton magnetic resonance spectra (for the alanine and valine complexes) are reported. For some salts of some of the complexes of optically active amino acids, one pure optical isomer could be obtained by slow crystallization from from the reaction solution. One optical isomer of the complexes containing optically active amino acids is present in the reaction mixture to a slightly greater extent than the other. The effects of hydroxide ion and heating on equilibration was studied. Assignments of absolute configurations were made from the CD spectra.     

Dichloro and amino acid cobalt(III) complexes of N,N′-diethylethylenediamine-N,N′-Di-α-butyrate ligand

A novel linear flexible ONNO-type tetradentate ligand, N,N′-diethylethylenediamine-N,N′-di-α-butyrate (deedba), and the dichloro, diaqua and amino acid (glycine, -alanine, -phenylalanine) cobalt(III) complexes of deedba have been synthesized via an H₂O₂ oxidation method. During the preparation of these complexes, the ligand has coordinated geospecifically to the cobalt(III) ion to give only one isomer, s-cis, which has been characterized by electronic absorption, ¹H NMR and IR spectra, and elemental analysis. It is of interest that this is one of the few Co^III(edda)X₂-type complex preparations, which gives only one isomer with geoselectivity.     

Transition metal ion complexes of thiosemicarbazones derived from 2-acetylpyridine. Part 3. The 3-hexamethyleneimine derivative

Summary Metal ion complexes of the thiosemicarbazone, 3-hexamethyleneimine-3-thiocarboxylic acid-2-[1-(2-pyridyl)-ethylidene]hydrazide (HLhexim) have been prepared and spectrally characterized. HLhexim coordinates primarily as the deprotonated tridentate ligand (i.e., pyridylN, azomethineN, and thione sulphur). The air oxidised cobalt(III) complex, [Co(LHexim)₂] (BF₄), was isolated from the preparation with cobalt(II) tetrafluoroborate, but other cobalt(II) salts yielded tetrahedral cobalt(II) compounds. Planar nickel(II) and copper(II) complexes were isolated from preparations with halide salts. Significant differences in the spectral properties of the various complexes are observed when compared to other thiosemicarbazones prepared from 2-acetylpyridine.     

Bis(glycinium) oxalate: evidence of strong hydrogen bonding

In the title 2:1 salt, 2C₂H₆NO₂⁺·C₂O₄²⁻, the glycine mol­ecule is in the cationic form with a positively charged amino group and an uncharged carboxylic acid group. The doubly charged oxalate anion lies across a crystallographic inversion centre. One of the reasons why the 1:1 glycinium oxalate salt has a higher melting point than the title compound may be the difference in their hydrogen‐bonding patterns. A database search for salts formed between amino acids or substituted amino acids and oxalic acid revealed that, in most of the structures, the conformation about the O=C—OH bond is synplanar. d ‐Tryptophan oxalate is the only example where the OH group of a semi‐oxalate adopts an anti­planar conformation. The 2:1 stoichiometry seen in the present salt is observed only in the salts of dl ‐serine, dl ‐aspartic acid and betaine with oxalic acid.     

Synthesis and Thermal Conversions of Unsaturated Cobalt(II) Monocarboxylates: Precursors for Metal Polymer Nanocomposites

Cobalt(II) salts of unsaturated monocarboxylic acids (acrylic acid, methacrylic acid, sorbic acid, 4-pentynoic acid, crotonic acid, linoleic acid, and oleic acid) are prepared. The prepared compounds are characterized by elemental analysis, IR spectroscopy, thermogravimetry, and differential scanning calorimetry. Cobalt-containing nanocomposites are produced by the thermal decomposition of the prepared carboxylates and characterized by elemental analysis, IR spectroscopy, scanning and transmission electron microscopy, energy dispersive X-ray spectroscopy, and X-ray powder diffraction. The enthalpies of reaction (ΔH_r°) for the formation of cobalt(II) salts of unsaturated monocarboxylic acids are calculated by the PM3 semiempirical quantum-chemical method. A correlation is found between the mean diameter (d_mean) of nanoparticles in nanocomposites and ΔH_r°.     

Separation of Cobalt (III) Bis(ethylenediamine) Amino Acid Complexes by Reversed Phase HPLC

Abstract

Methods for the rapid analysis of amino acid cobalt (III) bis(ethylenediamine) complexes by reversed phase high performance liquid chromatography (HPLC) are described with mobile phases containing the pairing ions, p-toluenesulphonate and hexanesulphonate. Under these conditions, the amino acid cobalt (III) bis(ethylenediamine) complexes elute in order of the relative hydrophobicities of the parent amino acids which suggests that the amino acid side chain makes a significant contribution to the retention mechanism. At high sample loadings, these complexes shows a concentration dependent peak splitting effect divergent to that normally experienced with inadequate buffering capacity of the pairing ion reagent.     

Characterization of complexes involved in the spectrophotometric determination of cobalt with 4-(2-pyridylazo)resorcinol

Complex species involved in the spectrophotometric determination of cobalt with 4-(2-pyridylazo)resorcinol (PAR = H₂R) were studied in solution and in the solid state. An anionic [Co(III)R₂]^- species was extracted from aqueous solution in chloroform by tetraphenylarsonium or tetraphenylphosphonium chloride. Stable tetraphenylarsonium and tetraphenylphosphonium salts of di-4-(2-pyridylazo)resorcinolo cobaltate(III) with the formula [(C₆H₅)₄X][Co(III)R₂] where X=As.P; and R=C₁₁H₇N₃O₂^2-, were isolated from the chloroform phase. The complexes were characterized by elemental analyses, visible, i.r., p.m.r., e.s.r. spectra, x-ray powder photographs, magnetic susceptibility and conductivity measurements. The spectral evidence and magnetic properties indicate a tridentate coordination of two 4-(2-pyridylazo) resorcinol dibasic anions, bonded to cobalt(III) in a symmetric arrangement with both azo groups coordinated to the cobalt atom through a single nitrogen lone pair.     

Facile Synthesis of Biologically Active Peptides Using Phase Transfer Reagents as C-Terminal Protecting Group

Phase-transfer reagents (basic, neutral, and acidic) can temporarily protect carboxyl groups by salt formation of C-terminal free amino acids or peptides during peptide synthesis. The salts of amino acids or peptides behave as RNH₂ rather than RNH₃⁺. At least there is a sufficient concentration of the free amine to act as a nucleophile under the reaction conditions. Many biologically active small peptides have been synthesized by this procedure. No racemization was detected. Unusual amino acids such as β-alanine, and ε-aminohexanoic acid can be incorporated into peptides in high yields.     

Complexes of 2-acetylpyridinesemicarbazone and 2-acetylpyridinethiosemicarbazone with cobalt(II), chromium(III) and copper(II)

Summary The synthesis and characterization of 2-acetylpyridine-semicarbazone (apsc) and 2-acetylpyridinethiosemicarbazone (aptsc) and their complexes with CoCl₂, CrCl₃ and CuCl₂ are reported. These compounds were characterized on the basis of elemental analyses, electronic and i.r. spectra, magnetic moments and conductivity measurements. The molar conductivities in dimethyl formamide indicate the non-ionic nature of the metal chelates. An octahedral structure is proposed for the chromium(III) chelate-complexes, tetrahedral for the copper(II) compounds and tetrahedral or octahedral for the cobalt(II). Apsc and aptsc are bidentate but with different donors, though aptsc is monodentate in its complex with CrCl₃.     

Preparation and characterization of a new SNO ligand derived from ethanebis(thioamide) and 2-hydroxybenzaldehyde, and its Cu(II), Co(II), and Rh(III) metal complexes

A new Schiff base N-[(E)-(2-hydroxyphenyl)methylidene]-N’-[(Z)-(2-hydroxyphenyl)methylidene]ethanebis(thioamide) (L_C) containing sulfur, nitrogen, and oxygen atoms has been synthesized by condensation of ethanebis(thioamide) with 2-hydroxybenzaldehyde. Metal complexes were synthesized by reaction of the new ligand with copper(II) and cobalt(II) as nitrate salts and with rhodium(III) as chloride salt, using hot absolute ethanol as solvent. All the new compounds were characterized by use of different physicochemical techniques including UV–visible spectroscopy, magnetic susceptibility, IR spectroscopy, molar conductance, and determination of metal content. It is proposed the paramagnetic copper and cobalt complexes adopt octahedral geometry whereas the diamagnetic rhodium complex has octahedral geometry.     

Reactivity trends of cobalt(III) complexes towards various amino acids based on the properties of the amino acid alkyl chains

The reactivity of the cobalt(III) complexes dichlorido[tris(2‐aminoethyl)amine]cobalt(III) chloride, [CoCl₂(tren)]Cl, and dichlorido(triethylenetetramine)cobalt(III) chloride, [CoCl₂(trien)]Cl, towards different amino acids (l ‐proline, l ‐asparagine, l ‐histidine and l ‐aspartic acid) was explored in detail. This study presents the crystal structures of three amino acidate cobalt(III) complexes, namely, (l ‐prolinato‐κ²N,O)[tris(2‐aminoethyl)amine‐κ⁴N,N′,N′′,N′′′]cobalt(III) diiodide monohydrate, [Co(C₅H₈NO₂)(C₆H₁₈N₄)]I₂·H₂O, I , (l ‐asparaginato‐κ²N,O)[tris(2‐aminoethyl)amine‐κ⁴N,N′,N′′,N′′′]cobalt(III) chloride perchlorate, [Co(C₄H₇N₂O₃)(C₆H₁₈N₄)](Cl)(ClO₄), II , and (l ‐prolinato‐κ²N,O)(triethylenetetramine‐κ⁴N,N′,N′′,N′′′)cobalt(III) chloride perchlorate, [Co(C₄H₇N₂O₃)(C₆H₁₈N₄)](Cl)(ClO₄), V . The syntheses of the complexes were followed by characterization using UV–Vis spectroscopy of the reaction mixtures and the initial rates of reaction were obtained by calculating the slopes of absorbance versus time plots. The initial rates suggest a stronger reactivity and hence greater affinity of the cobalt(III) complexes towards basic amino acids. The biocompatibility of the complexes was also assessed by evaluating the cytotoxicity of the complexes on cultured normal human fibroblast cells (WS1) in vitro. The compounds were found to be nontoxic after 24 h of incubation at concentrations up to 25 mM.     

The (salophen)-bridged Fe/Cr (III) capped complexes with triphenylene core: Synthesis and characterization

This article describes synthesis of the difference carboxylic acid derivatives of triphenylene and its complexation properties with Fe/Cr (III)-salophen. For this purpose, the carboxylic acid derivatives of 2,3,6,7,10,11-hexahydroxytriphenylene were synthesized and then reacted with four new Fe(III) and Cr(III) complexes involving tetradenta Schiff bases bis(salicylidene)-o-phenylenediamine-(salophenH₂). The prepared compounds were characterized by means of elemental analysis carrying out infrared spectroscopy (IR), thermogravimetric analysis (TG), nuclear magnetic resonance (¹H NMR), elemental analysis and magnetic susceptibility measurement. The complexes can also be characterized as low-spin distorted octahedral Fe(III) and Cr (III) bridged by carboxylic acids.     

Synthetic analogues of polynucleotides—XIII: The resolution of dl-β-(thymin-1-yl)alanine and polymerisation of the β-(thymin-1-yl)alanines

dl-β-(Thymin-1-yl)alanine has been resolved into d(+) and l(?) forms. The pure d(+) form was obtained by fractional crystallisation of the (+)α-methylphenylethylamine salts of the α-N-formyl derivatives. The pure l(?) isomer was obtained on a small scale by chromatography of the same salts. The optically active amino acids and the dl-mixture were polymerised by the mixed anhydride procedure to give polymers which showed no evidence of base stacking or of interaction with polyadenylic acid. The molecular weights of the polymers were in the range 2–4 × 10³. These were determined by end group assay which involved the synthesis of α-N-(2,4-dinitrophenyl)-dl-β-(thymin-1-yl)alanine as a standard.     

Recyclable synthesis of mesityl iodonium(III) salts

An efficient protocol for C–H condensation of hypervalent iodine compounds toward arenes in fluoroalcohols has been applied to the recyclable preparation of mesityl iodonium(III) salts. The electrophilicities of [hydroxy(tosyloxy)iodo]mesitylene (MesI(OH)OTs) and iodomesitylene diacetate (MesI(OAc)₂) are suitably enhanced in 2,2,2-trifluoroethanol. A series of nucleophilic aromatic compounds react smoothly with MesI(OH)OTs and MesI(OAc)₂ or in situ hypervalent iodine(III) species, generated from iodomesitylene, to provide the target mesityl iodonium(III) salts in good yields at room temperature with broad functional group tolerance. This C–H condensation strategy merits high para-regioselectivities during the diaryliodonium(III) salt formation, but the major limitation in the case of low-reactive aromatic substrates is byproduct formation resulting from the self-condensation of the nucleophilic mesitylene ring in MesI(OH)OTs and MesI(OAc)₂.     

Densities of aqueous solutions containing model compounds of amino acids and ionic salts at T = 298.15 K

Densities of amino acids in aqueous and in aqueous electrolyte solutions have been measured by a high precision vibrating tube digital densitometer at T = 298.15 K under atmospheric pressure. The investigated systems contained amino acids of zwitterionic glycine peptides: glycine (Gly), diglycine (Gly₂), triglycine (Gly₃), and tetraglycine (Gly₄) and cyclic glycylglycine (c(GG)) with electrolytes of potassium chloride (KCl), potassium bromide (KBr) and potassium acetate (KAc). In this series of measurements, the aqueous samples were prepared with various concentrations of the amino acids, up to saturated conditions, and over salt concentrations from 1 to 4 M. The density increments resulting from the addition of the different model compounds of amino acids and the ionic salts were investigated, respectively. An empirical linear combination equation with an augmented term to account the interactions between amino acid and ionic salt was used to quantitatively correlate the experimental densities over the entire concentration ranges.     

Kinetics and mechanism of Os(VIII)-catalyzed hexacyanoferrate(III) oxidation of α amino acids in alkaline medium

The kinetics of the Os(VIII)-catalyzed oxidation of glycine, alanine, valine, phenylalanine, isoleucine, lycine, and glutamic acid by alkaline hexacyanoferrate(III) reveal that these reactions are zero order in hexacyanoferrate(III) and first order in Os(VIII). The order in amino acid as well as in alkali is 1 at [amino acid] ?2.5 × 10^?2M and [OH^?] ?1.3 × 10^?M, but less than unity at higher concentrations of amino acids or alkali. The active oxidizing species under the experimental conditions is OsO₄(H₂O) (OH)^?. The ferricyanide is merely used up to regenerate the Os(VIII) species from Os(VI) formed during the reaction. The structural influence of amino acids on the reactivity has been discussed. The amino acids during oxidation are shown to be degraded through intermediate keto acids. The kinetic data are accommodated by considering the interaction between the conjugate base of the amino acids and the active oxidizing species of Os(VIII) to form a transient complex in the primary rate-determining step. The catalytic effect of hexacyanoferrate(II) has been rationalized.     

Hexafluorosilicates of bis(carboxypyridinium) and bis(2-carboxyquinolinium)

The preparation and characterization of three isomeric carboxypyridinium and carboxyquinolinium hexafluorosilicate salts is described. The salts of the general formulas (LH)₂[SiF₆] (I-III, L = 2-carboxypyridine, 3-carboxypyridine, 4-carboxypyridine) and (LH)₂[SiF₆]·2H₂O (IV, L = 2-carboxyquinoline) were prepared from the protonation reaction of the corresponding pyridine carbonic acid by the fluorosilicic acid. The compounds were characterized by IR, mass-spectrometry, thermogravimetric analysis, solubility data, and in the case of III by X-ray crystallography. The relationship between the salts solubility and the H-bonding system was analysed.     

Extraction-polarographic determination of cobalt(II) and nickel(II) as 2,2′-bipyridine complexes in acetonitrile

The tris(2,2′-bipyridine)cobalt(II) complex gives a reversible d.c. wave with E$\text{1}\text{2}$ = ?1.02 V vs. SCE and a sharp differential pulse peak at E_p = ?1.03 V in a salted-out acetonitrile phase. A simple selective method is described for the determination of cobalt(II); down to 0.25 μg of cobalt(II) can be determined in presence of large amounts of Ni, Zn, Cd, Pb, and Cu; iron(III) can be masked with sodium fluoride. The method is applicable to the determination of >0.0l% cobalt in nickel salts and >5 × 10^?5% cobalt in iron salts. Nickel(II) can also be extracted from aqueous solution and determined by differential pulse polarography, even in presence of a 20-fold amount of cobalt(II) by masking with EDTA; >0.01% of nickel in cobalt salts can be determined reproducibly.