Pivalate Research Articles

New heterometallic pivalates with FeIII and ZnII ions: Synthesis, structures, magnetic, thermal properties

Techniques for synthesizing Zn(II)-Fe(III) heterometallic molecular complexes [Fe2Zn4O2(Piv)10] (1), [Fe4Zn3O3(Piv)12(H2O)]·1.5Et2O (2) and [Fe3Zn2O2(Piv)9(1,10-phen)] (3) (where HPiv is pivalic acid, 1,10-phen – C12H8N2) have been developed. It has been found that recrystallization of the solid product formed from reaction mixture of Fe(NO3)3, Zn(NO3)2, KOH and HPiv (in the 3:2:13:34 ratio) in water («Reagent A») from acetone results in hexanuclear complex 1, whereas thermolysis of «Reagent A» at 130°C in air followed by crystallization of the thermolysis products from ether makes it possible to isolate complex 2. It has been found that dissolution of thermolyzed «Reagent A» in MeCN in the presence of 1,10-phenanthroline leads to formation of complex 3. The structures of complexes 1–3 were determined by single crystal X-ray diffraction analysis. The doublet Mössbauer spectra of complexes 1 and 2 correspond to high-spin Fe3+ ions in an octahedral environment of oxygen atoms, while the non-equivalence of the environment of iron ions in compound 3 (FeO6 and FeO4N2) is reflected by two observed doublets with different intensities. Based on the results of magnetic data simulation and quantum-chemical calculations, it has been shown that antiferromagnetic exchange coupling exists in complexes 1 and 2 (J12=−3.05cm−1 for 1 and J12=−0.4, J13=−13.5, J23=−3.6, J24=−27.2 and J34=−30.1cm−1 for 2). The value of the exchange integral between pairs of metal ions correlates with the Fe-O distances and the Fe-O-Fe angles in the bridging oxo ligands. Processes of thermal destruction have been studied for complexes 1 and 2 in argon atmosphere in the temperature range of 25–500°C.

Development of salt and pH–induced solidified floating organic droplets homogeneous liquid–liquid microextraction for extraction of ten pyrethroid insecticides in fresh fruits and fruit juices followed by gas chromatography-mass spectrometry

A new microextraction method named salt and pH–induced homogeneous liquid-liquid microextraction has been developed in a home–made extraction device for the extraction and preconcentration of some pyrethroid insecticides from different fruit juice samples prior to gas chromatography–mass spectrometry. In the present work, an extraction device made from two parallel glass tubes with different lengths and diameters was used in the microextraction procedure. In this method, a homogeneous solution of a sample solution and an extraction solvent (pivalic acid) was broken by performing an acid–base reaction and the extraction solvent was produced in whole of the solution. The produced droplets of the extraction solvent went up through the solution and solidified using an ice-bath. They were collected without centrifugation step. Under the optimum conditions, limits of detection and quantification were obtained in the ranges of 0.006–0.038, and 0.023–0.134ngmL–1, respectively. The enrichment factors and extraction recoveries of the selected analytes ranged from 365–460 to 73–92%, respectively. The relative standard deviations were lower than 9% for intra– (n = 6) and inter–day (n = 4) precisions at a concentration of 1ngmL–1 of each analyte. Finally, some fruit juice samples were effectively analyzed by the proposed method.

Ketone Formation from Carboxylic Acids by Ketonic Decarboxylation: The Exceptional Case of the Tertiary Carboxylic Acids.

For the reaction mechanism of the ketonic decarboxylation of two carboxylic acids, a β-keto acid is favored as key intermediate in many experimental and theoretical studies. Hydrogen atoms in the α-position are an indispensable requirement for the substrates to react by following this mechanism. However, isolated observations with tertiary carboxylic acids are not consistent with it and these are revisited and discussed herein. The experimental results obtained with pivalic acid indicate that the ketonic decarboxylation does not occur with this substrate. Instead, it is consumed in alternative reactions such as disintegration into isobutene, carbon monoxide, and water (retro-Koch reaction). In addition, the carboxylic acid is isomerized or loses carbon atoms, which converts the tertiary carboxylic acid into carboxylic acids bearing α-proton atoms. Hence, the latter are suitable to react through the β-keto acid pathway. A second substrate, 2,2,5,5-tetramethyladipic acid, reacted by following the same retro-Koch pathway. The primary product was the monocarboxylic acid 2,2,5-trimethyl-4-hexenoic acid (and its double bond isomer), which might be further transformed into a cyclic enone or a lactone. The ketonic decarboxylation product, 2,2,5,5-tetramethylcyclopentanone was observed in traces (<0.2 % yield). Therefore, it can be concluded that the observed experimental results further support the proposed mechanism for the ketonic decarboxylation via the β-keto acid intermediate.

Synthesis, structure, and properties of a lantern-type dinuclear rhodium(II) complex cis-[Rh2(4-Me-pf)2(O2CCMe3)2], 4-Me-pf− = N,N′-di-p-tolylformamidinate anion

A lantern-type dinuclear complex cis-[Rh2(4-Me-pf)2(O2CCF3)2] (1) (4-Me-pf− = N,N′-di-p-tolylformamidinate anion) was reacted with an excess of pivalic acid in an aqueous NaOH solution with CHCl3/MeOH (1:3 vol./vol.) at room temperature for 24 h with stirring to give cis-[Rh2(4-Me-pf)2(O2CCMe3)2] (2). A single crystal obtained by recrystallization of 1 from an acetonitrile solution was employed for X-ray crystal structure analysis. The analysis showed that the obtained complex was a cis-[Rh2(4-Me-pf)2(O2CCMe3)2(MeCN)2] (2(MeCN)2) with a lantern-type dinuclear structure and a cis-(2:2) arrangement of the two formamidinato and two carboxylato ligands around the dirhodium(II) core, similar to the previously reported crystal structures for 1(H2O)2·0.5C6H6 and 1(MeCN)2. Complex 2 showed absorption bands at 613, 506, 435, and 344 nm in MeCN, while complex 1 showed the bands at 516, 460, and 326 nm in MeCN. All the bands observed for 1 and 2 were reasonably assigned using time-dependent density functional theory calculation. Moreover, it was confirmed that the electron-donating t-butyl groups on the carboxylato bridges of 2 give rise to negative shifts in the redox potentials (E 1/2 = 0.32 and 1.22 V (vs. SCE) in CH2Cl2) for Rh 2 II,II /Rh 2 II,III and Rh 2 II,III /Rh 2 III,III processes relative to those of 1 (E 1/2 = 0.71 and 1.47 V (vs. SCE) in CH2Cl2) that has electron-withdrawing fluorine groups on the carboxylate bridges.

Structure and magnetic properties of a Co6 cluster based on high-spin CoII ions

A novel hexanuclear CoII complex with the formula of {[Co6(μ3-OH)(Hdhbp)4(dhbp)2(piv)3]·5CH3CN} (1, H2dhbp = 6,6′-dihydroxy-2,2′bipyridine, Hpiv = pivalic acid) was obtained and characterized. Single-crystal X-ray analysis shows that complex 1 contains six crystallographic independent CoII ions, which are gathered in the shell to form a [Co6] cluster. The six CoII ions embrace two coordination environments: the distorted octahedron and the vacant octahedron. Magnetic susceptibility of complex 1 was measured and studied.

Alkoxo- and carboxylato-bridged hexanuclear copper(II) complex: Synthesis, structure and magnetic properties

Reaction of copper(II) nitrate trihydrate with N,N-dimethylethanolamine (dmea) and pivalic acid in methanol led to the hexanuclear copper(II) complex Cu6(η1:μ2-C4H10NO)4(η1:η1:μ2-C5H9O2)4(η1:μ1-C5H9O2)2(μ3-OH)2 (1). The crystal structure of 1 indicates that hexametallic centers are bridged by the μ3-alkoxo, dmea oxygens, and the μ2-dicarboxylato oxygen atoms of pivalate ions. Furthermore, in the asymmetric unit, three types of copper ions have been found labeled as Cu1, Cu2 and Cu3. The Cu2 takes a distorted octahedral shape, whereas Cu1 and Cu3 adopt square pyramidal geometries. The complex 1 shows strong antiferromagnetic interactions through the oxo groups within the dimeric units (J=−82.6 to −25.8cm−1) and weak antiferromagnetic couplings between the dimers (J=−10.9 and 0.8cm−1).

Heterometallic CoII-CoIII-MII alkoxido-bridged heptanuclear motifs (M = Cu, Zn). Syntheses, crystal structures and magnetic properties

Abstract Two new alkoxido-bridged heterometallic complexes of formula [CoIICoIII3CuII3(dea)6(CH3COO)3](ClO4)0.75(CH3COO)1.25 (1) and [CoII2CoIII2ZnII3(tea)2(piv)6(CH3O)2(OH)2(CH3OH)2]·H2O 2 (H2dea = diethanolamine, H3tea = triethanolamine and Hpiv = pivalic acid) have been assembled using aminoalcohol ligands. The cationic core in 1 possesses a threefold crystallographic axis, and it exhibits a set of three copper(II), one cobalt(II) and three cobalt(III) ions arranged as a hexagon of alternating copper(II) and cobalt(III) ions around the central cobalt(II) ion. Each edge of the hexagon is defined by a double alkoxido bridge, the outer one being bis-monodentate with copper(II)-cobalt(III) pair whereas the inner one adopts a tris-monodentate coordination mode linking the Cu(II)-Co(III) pair with the central cobalt(II) ion. The acetate groups act as bidentate ligands towards the copper(II) ions. The intramolecular cobalt(II)-copper(II) separation is 3.157 A. A hexagon of two cobalt(II), two cobalt(II) and two zinc(II) ions distributed along three types of edges with a central zinc(II) ion occurs in 2. A tris-modentate alkoxido bridge is involved in all edges together with another bis-monodentate alkoxido bridge (CoIII-CoII and CoII-ZnII pairs) and a carboxylate-pivalate bridge in the syn-syn conformation. The five coordination at each peripheral zinc(II) ion is completed by a monodentate carboxylate-pivalate ligand whereas a methoxo group allows to achieve the six-coordination at each cobalt(III) ion. The intramolecular cobalt(II)-cobalt(II) separation through the inner zinc(II) ion is 6.309 A. The magnetic properties of 1 and 2 have been investigated in the temperature range 1.9–300 K. The exchange interaction between the six-coordinate cobalt(II) and copper(II) ions through the double alkoxido bridges in 1 and that between the six-coordinate cobalt(II) ions across the diamagnetic zinc(II) ion in 2 are found to be ferromagnetic [J = +5.39(5) (1) and +1.05(2) cm−1 (2)], the accidental orthogonality between the interacting magnetic orbitals accounting for this behaviour in the two cases.

Aluminum hydroxocarboxylates in solution deposition of planarization alumina films

Aluminum hydroxocarboxylates derived from butyric, pivalic, valeric, and isovaleric acids were synthesized and characterized. The synthesized hydroxocarboxylates were suspended in isopropanol and reacted with diethylenetriamine and monoethanolamine, which acted as hydrolyzing and complex-forming agents, to obtain precursor solutions for chemical deposition of smooth amorphous alumina films on metal substrates.

A family of FeIII4LnIII4 clusters containing derivatised salicylaldoximate ligand: Syntheses, structures and magnetic properties

A family of octanuclear clusters [FeIII4LnIII4O2(OH)4(mosaoH)4 (Piv)4(N-mdea)4(H2O)2] [Ln=Y(1), Gd(2), Tb(3) and Dy(4), mosaoH2=3-Methyloxysalicylaldoxime, N-mdeaH2=N-methyl diethanolamine, pivH=pivalic acid] has been prepared by reactions of [Fe3O(piv)6(OH2)2(OH)]·H2O with Ln(NO3)3·6H2O, mosaoH2 and N-mdeaH2 ligands. The crystal structures of 1–4 were obtained, and their core can be described as two distorted tetrahedral subunits of [Fe2Ln2(μ4–O)] connected by a pair of μ3–OH− groups. A dc magnetic susceptibility study reveals that there exist strong antiferromagnetic interactions between the neibouring Fe atoms. Fitting of the susceptibility data of compound 1 containing diamagnetic YIII ions gives J=−127cm−1. Compound 4 exhibits frequency-dependent out-of-phase ac susceptibility signals indicative of slow magnetization relaxation.

Synthesis, helicity, and low infrared emissivity of optically active poly(N-propargylamide)s bearing stigmasteryl moieties

Novel chiral N-propargylamide based on stigmasterol (M1, HCCCH2NHCOCH2CH2COO-R, R = stigmasteryl) and achiral N-propargylamide based on pivalic acid (M2) were prepared and (co)polymerized with rhodium zwitterions catalyst in CHCl3 to afford helical polyacetylenes with moderate molecular weights (8997–26777) in good yields. The polymers were characterized by Fourier transform infrared spectroscopy (FT-IR), 1H nuclear magnetic resonance (1H NMR), gel permeation chromatography (GPC). Ultraviolet–visible spectroscopy (UV–Vis) and circular dichroism (CD) absorption spectra demonstrated that the as-prepared polymers could form helical structures with a preferential helicity. The formation of hydrogen bonds of poly(M1) in CHCl3 was investigated according to the solution sate IR spectroscopic data. The single-handed helical conformation and polymerization degree of the new-typed poly(N-propargylamide)s could be controlled by the changing the feed ratio of chiral and achiral monomers. Furthermore, the infrared emissivity values (0.536–0.798) of copolymers were investigated at 8–14 μm by the Infrared Emissometer.

1D cerium(III) coordination polymer with pivalate bridges: Synthesis, structure and magnetic properties

In the present work, synthesis, characterization, and properties of a new 1D-polymeric chain of [Ce(piv)3(MeOH)2]n (1D-Ce) are described. This polymeric structure was synthesized via reaction of Ce(NO3)3·6H2O with pivalic acid in presence of triethylamine. Crystal structure consists of cerium coordinated to eight oxygen atoms from five pivalate and two methanol moieties. Magnetic studies on the complex revealed a strong antiferromagnetic interaction between CeIII ions in the 1D chain.

Carnitine-related hypoglycemia caused by 3\xa0days of pivalate antibiotic therapy in a patient with severe muscular dystrophy: a case report

BackgroundLong-term treatment with antibiotics containing pivalic acid may decrease serum carnitine concentration and can sometimes be associated with severe hypoglycemia and encephalopathy in infants. Little has been reported, however, on severe hypocarnitinemia induced by acute administration in older children.Case presentationWe describe a 6-year-old Japanese girl with Fukuyama-type congenital muscular dystrophy who lost consciousness after 3 days of treatment with an antibiotic containing pivalic acid (cefditoren pivoxil). Investigations at the onset of unconsciousness revealed hypoglycemia (free plasma glucose concentration: 31 mg/dL) and hypocarnitinemia (serum free carnitine concentration: 6.2 μmol/L). Intravenous administration of glucose rapidly improved her symptoms without any complications. Serum free carnitine concentration was 29.0 μmol/L immediately prior to the initiation of cefditoren pivoxil. Computed tomography scanning showed severe peripheral skeletal muscle atrophy, indicating the likelihood of decreased carnitine stores in skeletal muscle.ConclusionsAlthough serum carnitine concentration can appear deceptively normal, skeletal muscle carnitine stores can be reduced in patients with severe muscular atrophy. Even a short course of a pivalate-containing antibiotic can lead to life-threatening hypocarnitinemia in older children with severe muscular dystrophy.

Microwave absorption and infrared emissivity of helical polyacetylene@multiwalled carbon nanotubes composites

Hybrids of polyacetylene (PA) with multiwalled carbon nanotubes (MWNTs) were fabricated by wrapping PA derivatives containing stigmasterol and pivalic acid moieties onto MWNTs walls. The PA derivatives with moderate molecular weights (Mn ~ 24409) were proved to adopt a single-handed helical structure stabilized by asymmetric hydrogen bonding force and stereo-hindrance effect. Convincing experimental results show that PA had been wrapped evenly on the surface of MWNTs without damaging their internal structures. Moreover, the helical structure of PA became more compact and ordered after wrapping around MWNTs. The incorporation of stigmasterol moieties could contribute to enhancing the microwave absorbing properties and decreasing infrared emissivities. PA@MWNTs showed a minimum reflection loss value of −20.65 dB at 9.7 GHz and the bandwidth of reflection loss less than −10 dB (90% absorption) was 3.2 GHz. Meanwhile, PA@MWNTs composites had a much lower infrared emissivity value (e = 0.503) than raw MWNTs. The efficient microwave absorption and low infrared emissivity might result from the synergistic effect of the extraordinary helical structure of PA and π-electronic interactions between the organic substituents and inorganic MWNTs walls, which provides a promising method to prepare materials with low infrared emissivities and excellent microwave absorption properties.

A new topology of hexanuclear Mn/Ln clusters: Synthesis, structures and magnetic properties

Reactions of manganese nitrate and lanthanide nitrate hexahydrate with 2-(hydroxymethyl)pyridine (hmpH) and trimethylacetic acid as co-ligands in the mixture solutions of acetonitrile and ethanol generated two hexanuclear Mn-Ln compounds [Mn4La2O2(hmp)7(tBuCO2)2.5(NO3)4.5] [Ln=La (1), Nd (2)]. Compounds 1 and 2 are isostructural and possess a core of [MnIII4LaIII2(μ4-O)(μ3-O)(μ3-OR)(μ2-O)7]2−, which comprises three face-sharing defected cubane units. The species are new additions to the Mn/Ln clusters and the broader class of 3d/4f molecular systems. The solid-state direct current magnetic susceptibility analyses indicate the antiferromagnetic interactions within two compounds. The systematic investigation summarized that the variation of auxiliary ligand carboxylate R group affects structural distortions and switch the magnetic behaviour.

Chemoselective N-acetylation of primary aliphatic amines promoted by pivalic or acetic acid using ethyl acetate as an acetyl donor

The combination of pivalic or acetic acid as a promoter and EtOAc as a solvent and acetyl donor proved to be efficient for the chemoselective N-acetylation of primary aliphatic amines to afford the corresponding acetamides. We developed a simple and convenient approach, which requires mild reaction conditions. Competitive inter- and intramolecular reactions between aliphatic amines, alcohols, and aromatic amines were examined, and chemoselectivity was achieved by adjusting the conditions of the reaction.

A novel LCMSMS method for quantitative measurement of short-chain fatty acids in human stool derivatized with 12C- and 13C-labelled aniline

A novel liquid chromatography tandem mass spectrometry (LCMSMS) method for the quantitative measurement of gut microbial-derived short-chain fatty acids (SCFAs) in human infant stool has been developed and validated. Baseline chromatographic resolution was achieved for 12 SCFAs (acetic, butyric, caproic, 2,2-dimethylbutyric, 2-ethylbutyric, isobutyric, isovaleric, 2-methylbutyric, 4-methylvaleric, propionic, pivalic and valeric acids) within an analysis time of 15min. A novel sequential derivatization of endogenous and spiked SCFAs in stool via 12C- and 13C-aniline respectively, facilitated the accurate quantitation of 12C-aniline derivatized endogenous SCFAs based on calibration of exogenously 13C-derivatized SCFAs. Optimized quenching of derivatization agents prior to LCMSMS analysis further reduced to negligible levels the confounding chromatographic peak due to in-line derivatization of unquenched aniline with residual acetic acid present within the LCMS system. The effect of residual acetic acid, a common LCMS modifier, in analysis of SCFAs has not been addressed in previous SCFA assays. For the first time, a total of 9 SCFAs (acetic, butyric, caproic, isobutyric, isovaleric, 2-methylbutyric, 4-methylvaleric, propionic and valeric acids) were detected and quantitated in 107 healthy infant stool samples. The abundance and diversity of SCFAs in infant stool vary temporally from 3 weeks onwards and stabilize towards the end of 12 months. This in turn reflects the maturation of infant SCFA-producing gut microbiota community. In summary, this novel method is applicable to future studies that investigate the biological roles of SCFAs in paediatric health and diseases.

Improved resistance of chemically-modified nanocellulose against thermally-induced depolymerization

The study demonstrated the improvement in the resistance of nanocellulose against thermally-induced depolymerization by esterification with benzoyl (BNZ) and pivaloyl (PIV). The change in the degree of polymerization (DP) and molecular weight distribution (MWD) after thermal treatment in nitrogen and in air was investigated using viscometry and gel permeation chromatography. BNZ and PIV nanocellulose esters without α-hydrogens gave higher DP and narrower MWD than pure bacterial cellulose; and the acetyl and myristoyl esters, which possess α-hydrogens. Results also showed that when depolymerization is suppressed, thermal discoloration is also reduced. Resistance against depolymerization inhibits the formation of reducing ends which can be active sites for thermal discoloration. Finally, the findings suggest that benzoylation and pivaloylation can be an excellent modification technique to improve the thermal stability of nanocellulose.

Role of Lewis acid additives in a palladium catalyzed directed C–H functionalization reaction of benzohydroxamic acid to isoxazolone

Metallic salts as well as protic additives are widely employed in transition metal catalyzed C-H bond functionalization reactions to improve the efficiency of catalytic protocols. In one such example, ZnCl2 and pivalic acid are used as additives in a palladium catalyzed synthesis of isoxazolone from a readily available benzohydroxamic acid under one pot conditions. In this article, we present some important mechanistic insights into the role of ZnCl2 and pivalic acid, gained by using density functional theory (M06) computations. Two interesting modes of action of ZnCl2 are identified in various catalytic steps involved in the formation of isoxazolone. The conventional Lewis acid coordination wherein zinc chloride (ZnCl2·(DMA)) binds to the carbonyl group is found to be more favored in the C-H activation step. However, the participation of a hetero-bimetallic Pd-Zn species is preferred in reductive elimination leading to Caryl-N bond formation. Pivalic acid helps in relay proton transfer in C-H bond activation through a cyclometallation deprotonation (CMD) process. The explicit inclusion of ZnCl2 and solvent N,N-dimethyl acetamide (DMA) stabilizes the transition state and also helps reduce the activation barrier for the C-H bond activation step. The electronic communication between the two metal species is playing a crucial role in stabilizing the Caryl-N bond formation transition state through a Pd-Zn hetero-bimetallic interaction.

Introduction of a Simple Second Tier Screening Test for C5 Isobars in Dried Blood Spots: Reducing the False Positive Rate for Isovaleric Acidaemia in Expanded Newborn Screening.

In 2015 the English Newborn Screening programme expanded to include Isovaleric Acidaemia (IVA). Screening is performed by flow injection analysis tandem mass spectrometry of isovalerylcarnitine. Isovalerylcarnitine is isobaric with pivaloylcarnitine which can be present in blood due to the use of pivalic ester pro-drugs or pivalic acid derivatives used as emollients in some nipple creams; the potential for false positives (FP) is well documented. A pilot study in England screened 438,164 babies, 18 had presumptive positive results but only 4 were confirmed as true positives (TP). We developed a simple test to separate the isobaric compounds and investigate these samples further.We studied newborn screening blood spots from 122 randomised controls and 34 infants with an initial raised C5 result. Dried blood spots were eluted with 30% acetonitrile (150μL) and injected into a Waters Acquity UPLC coupled to a Waters Premier XE tandem mass spectrometer operating in positive ion mode. Isocratic separation of isovalerylcarnitine, pivaloylcarnitine, valerylcarnitine and 2-methylbutyrylcarnitine was achieved within 8min. Assay performance characteristics were acceptable and non-parametric reference ranges (n=122) were determined for each analyte.If this method had been used as a second tier test for the 34 presumptive positive samples, the number of FP's would have reduced from 24 to 8 and the positive predictive value of the screening test would have increased from 29 to 56%. Introduction of this test into the screening protocol has the potential to significantly reduce FP results for IVA and prevent unnecessary anxiety.

Reaction of 2-(nitroamino)pyrimidin-4(3H)-one derivatives with arylamines of low basicity in pivalic acid

Pivalic acid was used as a solvent for aminolysis of poly-substituted 2-(nitroamino)-pyrimidin-4(3Н)-one derivatives with arylamines of low basicity. The reaction did not occur in the other solvents or without solvent. Aminolysis products were obtained in 51–59% yields.