Hydrogen‐bonding and C—H⋯π interactions in 7‐hydroxy‐3‐methoxy‐4‐methyl‐5,6,7,8‐tetrahydro­pyrido­[1,2‐c]pyrimidin‐1(9H)‐one

In the title compound, C₁₀H₁₄N₂O₃, a pyrimidine ring is fused with a piperidine ring. The pyrimidine ring is planar, whereas the piperidine ring adopts a half‐chair conformation. The molecules of the title compound are connected via O—H⋯O intermolecular hydrogen bonds into infinite zigzag chains. The pyrimidine ring is involved in three C—H⋯π interactions, which link the hydrogen‐bonded chains into a three‐dimensional framework.     

Synthesis,Spectrothermal Behaviour and Molecular Structure of Aquaorotatotriethanolaminenickel(II) Monohydrate

The aquaorotatotriethanolaminenickel(II) monohydrate, [Ni(HOr)(H₂O)(tea)]·H₂O ( 1 ), was synthesized and characterized by means of elementel analysis, IR and UV‐Vis, spectroscopy, magnetic susceptibility, thermal analysis and X‐ray diffraction techniques. The nickel ion in [Ni(C₅H₂N₂O₄)(H₂O)(N(C₂H₄OH)₃)] is chelated to the deprotonated N3 pyrimidine atom and to the carboxylate oxygen atom of the bidentate orotate dianion, and to the one nitrogen and two oxygen atoms of the tridentate triethanolamine molecule and its octahedral geometry is completed by an aqua ligand. It crystallizes in the monoclinic system, space group P2₁/c with lattice parameters a = 7.1528(5) Å, b = 19.4903(14) Å, c = 11.8085(8) Å, β = 106.237(5)°, V = 1580.55(19) ų, Z = 4. An extensive three dimensional network of O_w‐H…O, N‐H…O and O‐H…O hydrogen bonds, π‐π and π‐ring interactions are responsible for crystal stabilization. The decomposition reaction take places in the temperature range 20‐1000 °C in the static air atmosphere. Thermal decomposition of 1 proceeds in three stages.     

Dimorphism in (2Z)‐2‐benzyl­idene‐N,7‐dimethyl‐3‐oxo‐5‐phenyl‐2,3‐dihydro‐5H‐1,3‐thia­zolo[3,2‐a]pyrimidine‐6‐carboxamide

The title compound, C₂₂H₁₉N₃O₂S, crystallizes in two polymorphic forms having the same space group, viz. P, with Z′ = 2 and Z′ = 1. In both polymorphs, the planar thia­zole ring is fused cis with the dihydro­pyrimidine ring, the carbamoyl group is in an extended conformation with an anti­clinal orientation with respect to the pyrimidine ring, and the phenyl ring is attached to the pyrimidine ring approximately at a right angle. The two polymorphs have different inter­planar angles between the phenyl and thia­zole rings. The mol­ecules are linked by N—H⋯O and C—H⋯O hydrogen bonds.     

A study of the stability of pyrimidine series cytostatics,Ftorafur and 5-fluorouracil: The effect of oxidation on the stability of Ftorafur and 5-fluorouracil

The stability of 1% solutions of cytostatics Ftorafur and 5-fluorouracil was studied during oxidation with hydrogen peroxide in alkaline (0.1 N NaOH), acidic (0.1 N H₂SO₄), and weakly acidic (pH 5) solutions by thin-layer chromatography. The decrease in the cytostatic content was monitored spectrophotometrically in the uv region. The greatest decrease in the cytostatic content occurred in alkaline solutions, where the pyrimidine ring opened between N3 and C4 and between C6 and N1, with formation of urea.     

In situ FT-IR studies of NO decomposition on Pt/TiO2 catalyst under UV irradiation

Photodecomposition of NO on the well-dispersed Pt/TiO₂ catalyst under UV irradiation was studied by in situ DRIFT (Diffuse-Reflectance Infrared Fourier-Transform) spectroscopy. 2 wt% Pt/TiO₂ catalyst was prepared by photochemical deposition method. The photocatalytic activity of Pt/TiO₂ is highly dependent on its pretreatment. Although the catalyst exhibited a highly adsorption capability to NO after hydrogen reduction or thermal evacuation at 500°C, no evidence upon NO decomposition was observed under UV irradiation. While reducing the catalyst at 300°C in the hydrogen flow, it not only exhibited an intense NO adsorption but also conducted a direct decomposition of NO to N₂ and O₂ under UV irradiation. The hydrogen reduction at 200°C led to a weaker NO adsorption. During UV irradiation, the IR peaks of NO fully disappeared and N₂O was formed. It is concluded that the photochemical prepared Pt/TiO₂ catalyst after activating at mild reduction conditions is highly active for NO photodecomposition. The effective oxidation states of the active components, the surface structure and the reaction mechanisms will be discussed.     

3-Nitro-1-nitromethyl-1H-1,2,4-triazole

The title compound, C₃H₃N₅O₄, consists of three planar fragments twisted in relation to each other, namely a triazole ring, a nitro­methyl­ene group and a nitro group. Molecular conformation analysis shows that the first stage of thermal decomposition is a breakage of the H₂C—NO₂ bond. There are essential conformational differences in the mol­ecule in comparison with semi-empirical calculations.     

Ditopic halogen bonding with bipyrimidines and activated pyrimidines

The potential of pyrimidines to serve as ditopic halogen‐bond acceptors is explored. The halogen‐bonded cocrystals formed from solutions of either 5,5′‐bipyrimidine (C₈H₆N₄) or 1,2‐bis(pyrimidin‐5‐yl)ethyne (C₁₀H₆N₄) and 2 molar equivalents of 1,3‐diiodotetrafluorobenzene (C₆F₄I₂) have a 1:1 composition. Each pyrimidine moiety acts as a single halogen‐bond acceptor and the bipyrimidines act as ditopic halogen‐bond acceptors. In contrast, the activated pyrimidines 2‐ and 5‐{[4‐(dimethylamino)phenyl]ethynyl}pyrimidine (C₁₄H₁₃N₃) are ditopic halogen‐bond acceptors, and 1:1 halogen‐bonded cocrystals are formed from 1:1 mixtures of each of the activated pyrimidines and either 1,2‐ or 1,3‐diiodotetrafluorobenzene. A 1:1 cocrystal was also formed between 2‐{[4‐(dimethylamino)phenyl]ethynyl}pyrimidine and 1,4‐diiodotetrafluorobenzene, while a 2:1 cocrystal was formed between 5‐{[4‐(dimethylamino)phenyl]ethynyl}pyrimidine and 1,4‐diiodotetrafluorobenzene.     

A stacked pyrazolo­[3,4‐d]­pyrimidine‐based flexible mol­ecule: the effect on stacking of a bulky iso­propyl group in comparison with a methyl/ethyl group

In the crystal structure of 1,3‐bis(4,6‐diiso­propyl­sulfanyl‐1H‐pyrazolo­[3,4‐d]­pyrimidin‐1‐yl)­propane, C₂₅H₃₆N₈S₄, the pairs of pyrazolo­[3,4‐d]­pyrimidine rings in the mol­ecule stack as a result of intramolecular π–π interactions between the heterocyclic rings. The crystal packing also exhibits an intermolecular C—H...π interaction between one methyl group of an iso­propyl group and a pyrazolo­[3,4‐d]­pyrimidine ring.     

Cocrystals of the antibiotic trimethoprim with glutarimide and 3,3‐dimethylglutarimide held together by three hydrogen bonds

The antibiotic trimethoprim [5‐(3,4,5‐trimethoxybenzyl)pyrimidine‐2,4‐diamine] was cocrystallized with glutarimide (piperidine‐2,6‐dione) and its 3,3‐dimethyl derivative (4,4‐dimethylpiperidine‐2,6‐dione). The cocrystals, viz. trimethoprim–glutarimide (1/1), C₁₄H₁₈N₄O₃·C₅H₇NO₂, (I), and trimethoprim–3,3‐dimethylglutarimide (1/1), C₁₄H₁₈N₄O₃·C₇H₁₁NO₂, (II), are held together by three neighbouring hydrogen bonds (one central N—H...N and two N—H...O) between the pyrimidine ring of trimethoprim and the imide group of glutarimide, with an ADA/DAD pattern (A = acceptor and D = donor). These heterodimers resemble two known cocrystals of trimethoprim with barbituric acid and its 5,5‐diethyl derivative. Trimethoprim shows a conformation in which the planes of the pyrimidine and benzene rings are approximately perpendicular to one another. In its glutarimide coformer, five of the six ring atoms lie in a common plane; the C atom opposite the N atom deviates by about 0.6 Å. The crystal packing of each of the two cocrystals is characterized by an extended network of hydrogen bonds and contains centrosymmetrically related trimethoprim homodimers formed by a pair of N—H...N hydrogen bonds. This structural motif occurs in five of the nine published crystal structures in which neutral trimethoprim is present.     

Thermal decomposition of Pr[(C5H8NS2)(C12H8N2)]

The thermal behavior of the complex Pr[(C₅H₈NS₂)(C₁₂H₈N₂)] in a dry nitrogen flow was examined by TG-DTG analysis. The TG-DTG investigations indicated that Pr[(C₅H₈NS₂)(C₁₂H₈N₂)] was decomposed into Pr₂S₃ and deposited carbon in one step where Pr₂S₃ predominated in the final products. The results of non-isothermal kinetic calculations showed that the decomposition stage was the random nucleation and subsequent growth mechanism(n = 2/3), the corresponding apparent activation energyE was 115.89 kJ•mol⁻¹ and the pre-exponential constant In[A/s] was 7.8697. The empirical kinetics model equation was proposed as\(f(\alpha ) = \frac{3}{2}(1 - \alpha )[ - 1n(1 - \alpha )]^{\frac{1}{3}} \). The X-ray powder diffraction patterns of the thermal decomposition products at 800 °C under N₂ atmosphere show that the product can be indexed to the cubic Pr₂S₃ phase. The transmission electron microscopy (TEM) of the final product reveals the particle appearance of a diameter within 40 nm. The experimental results show that the praseodymium sulfide nanocrystal can be prepared from thermal decomposition of Pr[(C₅H₈NS₂)(C₁₂H₈N₂)].

     

Thermal analysis of 5′-deoxy-5′-iodo-2′,3′-O-isopropylidene-5-fluorouridine

The melting temperature, melting enthalpy, and specific heat capacities (C _p) of 5′-deoxy-5′-iodo-2′,3′-O-isopropylidene-5-fluorouridine (DIOIPF) were measured using DSC-60 Differential Scanning Calorimetry. The melting temperature and melting enthalpy were obtained to be 453.80 K and 33.22 J g^?1, respectively. The relationship between the specific heat capacity and temperature was obtained to be C _p/J g^?1 K^?1 = 2.0261 – 0.0096T + 2 × 10^?5 T ² at the temperature range from 320.15 to 430.15 K. The thermal decomposition process was studied by the TG–DTA analyzer. The results showed that the thermal decomposition temperature of DIOIPF was above 487.84 K, and the decomposition process can be divided into three stages: the first stage is the decomposition of impurities, the mass loss in the second stage may be the sublimation of iodine and thermal decomposition process of the side-group C₄H₂O₂N₂F, and the third stage may be the thermal decomposition process of both the groups –CH₃ and –CH₂OCH₂–. The obtained thermodynamic basic data are helpful for exploiting new synthetic method, engineering design, and commercial process of DIOIPF.     

Two carbamoyl‐substituted di­hydro­pyrimidines: potential mimics of di­hydro­pyridine calcium channel blockers

The structures of two conformationally similar 1,4‐di­hydro­pyrimidines with a novel carbamoyl substitution, viz. 6‐methyl‐5‐(N‐methyl­carbamoyl)‐4‐phenyl‐1,2,3,4‐tetrahydro­py­rimidine‐2‐thione monohydrate, C₁₃H₁₅N₃OS·H₂O, (I), and 4‐(4‐chloro­phenyl)‐6‐methyl‐5‐(N‐methyl­carbamoyl)‐1,2,3,4‐tetra­hydro­pyrimidine‐2‐thione monohydrate, C₁₃H₁₄ClN₃OS·H₂O, (II), exhibit the structural features of 1,4‐di­hydro­pyridine calcium channel blockers. In both structures, the pyrimidine ring adopts a flattened boat conformation and the carbamoyl side chain is in an extended conformation with an anticlinal orientation. The phenyl ring occupies a pseudo‐axial position with respect to the pyrimidine ring in these structures. Both compounds crystallize with one mol­ecule of water, which participates in a two‐dimensional hydrogen‐bonding network. The mol­ecules are linked into dimers by N—H·S hydrogen bonds in both structures.     

Dynamic and structural models of pyrimidine in the lowest excited singlet state

Problems on the normal vibrations of pyrimidine in the ground and excited states are solved. The matrices of rotation and shift of normal coordinates due to electronic excitation and Franck-Condon integrals are calculated. The vibronic spectra of pyrimidine are interpreted. Based on this interpretation, bond lengths and bond angles in the electronically excited first singlet state of the molecule are calculated: C₁C₂ 1.388 å, C₂N₃ 1.366 å, N₃C₄ 1.352 å, C-H 1.099 å; C₆C₁C₂ 105.5?, N₃C₄N₅ 127.8?, H₂C₂N₃ 110.1?.     

Mass spectra of 2,3-polymethylene-3,4-dihydroquinazolin-4-ones with substituents at C9

Summary The main fragments in the mass spectra of the 2,3-polymethylene-3,4-dihydroquinazolin-4-one with six- and seven-membered alicyclic rings are formed by the decomposition of ring C through the stage of the cleavage of the C₉-C₁₀ bond, while the compound with a five-membered ring ejects a hydrogen atom.A hydroxy group at C₉ initiates the appearance of fragments due to the initial cleavage of the C₂-C₉ bond. In the spectra of the halogen and acetoxy derivatives the fragmentation of the alicyclic ring is suppressed and the main fragmentation pathway is the splitting out of the substituent. The hypothesis of the protonation of the N₁ nitrogen atom has been adopted to explain the stability of a number of the ions.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 180–187, March–April, 1979.     

Thermal analysis of prednicarbate and characterization of thermal decomposition product

In the present work, the thermal behavior of prednicarbate was studied using DSC and TG/DTG. The solid product remaining at the first decomposition step of the drug was isolated by TG, in air and N₂ atmospheres and was characterized using LC-MS/MS, NMR, and IR spectroscopy. It was found that the product at the first thermal decomposition step of prednicarbate corresponds to the elimination of the carbonate group bonding to C₁₇, and a consequent formation of double bond between C₁₇ and C₁₆. Structure elucidation of this degradation product by spectral data has been discussed in detail.     

1:1 Hetero‐assembly of 2‐amino­pyrimidine and (+)‐camphoric acid

In the title cocrystal, 2‐aminopyrimidine–(+)‐camphoric acid (1/1), C₄H₅N₃·C₁₀H₁₆O₄, the 2‐amino­pyrimidine forms two eight‐membered hydrogen‐bonded rings with two different camphoric acid mol­ecules. This results in infinite wave‐like chains of mol­ecules in which neighbouring chains are connected by weak C—H?O contacts. The five‐membered ring in the acid mol­ecule adopts a half‐chair conformation.     

Thermal decomposition and kinetic studies on a binuclear copper(II)—Urea complex

A binuclear copper(II)—urea complex was synthesized and its structure was established from elemental analyses, IR, UV and visible spectroscopy and magnetic susceptibility measurements to be [OC(NH₂)₂Cu(OH)₂]₂. The kinetics of the thermal decomposition of the complex were studied by recording thermogravimetric measurements in streams of nitrogen and oxygen. TG analysis showed three main steps of decomposition, leading to Cu₂O formation in the final stage.     

The first bis(orotato–N,O) complex: Synthesis,crystal structure,spectroscopic and thermal characterization of (chaH)2[Cu(HOr–N,O)2(cha)] · 2H2O (cha = cyclohexylamine and HOr = orotate(2−))

The novel bis(cyclohexylaminium) cyclohexylaminebis(orotate–N,O)cuprate(II) dihydrate, (C₆H₁₅N)₂[Cu(C₅H₂N₂O₄)₂(C₆H₁₄N)] · 2H₂O, has been prepared and characterized by elemental analysis, magnetic measurements, FT-IR and UV–Vis spectroscopy, thermal analysis and X-ray diffraction. The Cu(II) complex crystallizes in the monoclinic space group P2₁/c. The copper atom in the five-coordinated (chaH)₂[Cu(HOr–N,O)₂(cha)] · 2H₂O is chelated by a deprotonated pyrimidine nitrogen atom and carboxylate oxygen atom as a bis(bidentate) ligand and the cyclohexylamine ligand completes the square-pyramidal coordination. The thermal decomposition of the complex has been predicted by the help of thermal analysis (TG, DTG and DTA).     

Hydrogen‐bonded sheet structures in neutral,anionic and hydrated 6‐amino‐2‐(morpholin‐4‐yl)‐5‐nitrosopyrimidines

In each of 6‐amino‐3‐methyl‐2‐(morpholin‐4‐yl)‐5‐nitrosopyrimidin‐4(3H)‐one, C₉H₁₃N₅O₃, (I), morpholin‐4‐ium 4‐amino‐2‐(morpholin‐4‐yl)‐5‐nitroso‐6‐oxo‐1,6‐dihydropyrimidin‐1‐ide, C₄H₁₀NO⁺·C₈H₁₀N₅O₃⁻, (II), and 6‐amino‐2‐(morpholin‐4‐yl)‐5‐nitrosopyrimidin‐4(3H)‐one hemihydrate, C₈H₁₁N₅O₃·0.5H₂O, (III), the bond distances within the pyrimidine components are consistent with significant electronic polarization, which is most marked in (II) and least marked in (I). Despite the high level of substitution, the pyrimidine rings are all effectively planar, and in each of the pyrimidine components, there are intramolecular N—H...O hydrogen bonds. In each compound, the organic components are linked by multiple N—H...O hydrogen bonds to form sheets of widely differing construction, and in compound (III) adjacent sheets are linked by the water molecules, so forming a three‐dimensional hydrogen‐bonded framework. This study also contains the first direct geometric comparison between the electronic polarization in a neutral aminonitrosopyrimidine and that in its ring‐deprotonated conjugate anion in a metal‐free environment.     

Influence of fullerene on the kinetics of thermal and thermo-oxidative degradation of high-density polyethylene by capturing free radicals

The influence of fullerene (C₆₀) on the thermal and thermal-oxidative degradation of high-density polyethylene (HDPE) was studied using non-isothermal thermogravimetric analysis under nitrogen (N₂) and air atmosphere. Kinetic parameters of the degradation were evaluated using the Flynn–Wall–Ozawa method, which does not require the knowledge of the reaction mechanism. The results showed that the addition of C₆₀ enhanced the thermal stability of HDPE and increased the activation energy both in N₂ and air atmosphere and especially affected the initial stage of degradation. In N₂, C₆₀-trapped carbon-centered radical originated from the degradation of HDPE to improve the thermal stability and increase the activation energy. While in air, C₆₀ trapped the alkyl radicals and alkyl peroxide radicals to inhibit the hydrogen abstraction (especially the initial stage of thermo-oxidative degradation) and form more stable species, which improved the thermal stability and increased the activation energy during the thermal degradation of HDPE. Comparing with that of pure HDPE, the changes of activation energy for HDPE/C₆₀ nanocomposites were higher in air than in N₂, especially in the initial stage.