Guanidine Carbonate Research Articles

Methanolysis of triacylglycerols by organic basic catalysts

AbstractMethanolysis of rapeseed and soybean oil was studied using organic basic catalysts at boiling with reflux. The molar ratio methanol/free fatty acids (FFA) amounted to approx 2.8 : 1. The catalyst (guanidine carbonate) is used at concentrations between 0.5 and 1.3 wt‐% with respect to the oil. During boiling at reflux, guanidine carbonate disintegrates into guanidine and gaseous carbon dioxide. This is a very special reaction; other alcohols such as ethanol, propanol, etc. do not react in this way with guanidine carbonate. Under these conditions, the reaction mixture consists of two phases. The catalyst is mainly dissolved in the methanol phase. The rate of the phase transfer reaction is increased by stirring. With guanidine carbonate as a catalyst, neutralized rapeseed oil yielded, within 45 min and in one step, a product that meets the European Norm for biodiesel. Degummed and dried crude rapeseed oil contains ca. 1 wt‐% FFA, whereas crude degummed and dried soybean oil contains 0.3–0.7 wt‐% FFA. During catalysis with guanidine carbonate, the FFA are transformed into their methyl esters to about 60–70% at low concentrations in the crude oil (approximately up to 1–1.5%). Neutralization of the degummed and dried crude oil proved to be unnecessary in such cases.

Synthesis of 2‐[4‐(10H‐Substituted Phenothiazine‐3‐yl)‐6‐Pyrimidin‐2‐Phenylthiol/ol/amine/thiol] Pyrroles

2‐[4‐Hydroxy benz‐1(propene‐1‐one)]Pyrrole II on treatment with phenyl thiourea, guanidine carbonate, urea and thiourea in alcoholic KOH yielded compounds III, IV, V, VI which on treatment with different aryl anilines gave compounds VII, VIII, IX, X which under goes cyclisation with sulphur and iodine to give 2‐[4‐(10H‐substituted phenothiazine‐3‐yl)‐6‐pyrimidin‐2‐phenylthiol/‐ol/‐amine/‐thiol] pyrrole XI(a‐j), XII(a‐j), XIII(a‐j) and XIV(a‐j) respectively. The structural products were characterized by elemental analysis and spectral data.

Guanosine analog in the pyrido[2,3-d]pyrimidine ring system As a potential Toll-like receptor agonist

The synthesis of a guanosine analog in the pyrido[2,3-d]pyrimidine ring system has been accomplished by glycosylation of the preformed aromatic heterocyclic base, which was prepared in 2 steps by condensation of methyl acrylate with guanidine carbonate and methyl cyanoacetate in the presence of sodium methoxide, followed by dehydrogenation. The analog was evaluated in vitro for its ability to modulate the innate immune response by acting as an agonist or as an antagonist of Toll-like receptor (TLR) signaling by measuring cytokine induction or inhibition of induction, respectively, in mouse bone marrow-derived macrophages. Despite its structural similarity to 7-thia-8-oxoguanosine, a known TLR7 agonist, the analog was found to antagonize TLR7-induced cytokine induction in this cell-based assay.

Wplyw budowy polimerowych katalizatorow utleniania na ich aktywnosc katalityczna

The effect of the structure of particular group of polymeric catalysts of the oxidation process on their catalytic activity, in the model reaction of hydroquinone oxidation to p-benzoquinone with hydrogen peroxide, was investigated. Two series of terpolymers of acrylonitril (AN) and vinyl acetate (VA) crosslinked with either divinylbenzene (DVB) or trihydroxymethylpropane triacrylate (TMPA) or trihydroxymethylpropane trimethacrylate (TMPMA) (Table 2) were obtained in suspension polymerization. Dependently on the type of crosslinking monomer the products showed either the gel structure or porous one. In two-stage process the nitrile groups of terpolymer were subjected to aminolysis with hydrazine and amino groups obtained in this way were modified with thiourea in the presence of alkyl iodide (Scheme A). The supports containing aminoguanidyl, carboxyl or hydroxyl groups were obtained (Table 1 and 3) and their structures were characterized using FT-IR method. The proper catalysts were prepared via sorption of Cu(II) ions on these supports. Some parameters of these catalysts and of the catalysts prepared in one-stage aminolysis of terpolymers with guanidine carbonate or aminoguanidine carbonate were compared. They were: hydroquinone conversion degree (LH2Q), yield of quinone (YQ) as a main product and selectivity of the catalysts calculated on this basis (Table 4 and 5, Fig. 5 and 6). The catalysts crosslinked with DVB and subjected to one-stage modification showed the highest activity and selectivity (close to 100 %). In all cases the catalysts with aminoguanidyl groups were more active than those with hydrazine groups not subjected further modification. The results obtained show that the conditions encouraging the formation of N2O2 complexes as well as advantageous microenvironment formed by uncomplexed functional groups determine the activity and selectivity of the catalysts investigated.

Nanometer-Scale Ion Aggregates in Aqueous Electrolyte Solutions: Guanidinium Carbonate

Neutron diffraction with isotopic substitution (NDIS) experiments and molecular dynamics (MD) simulations have been used to characterize the structure of aqueous guanidinium carbonate (Gdm2CO3) solutions. The MD simulations found very strong hetero-ion pairing in Gdm2CO3 solution and were used to determine the best structural experiment to demonstrate this ion pairing. The NDIS experiments confirm the most significant feature of the MD simulation, which is the existence of strong hetero-ion pairing between the Gdm+ and CO3(2-) ions. The neutron structural data also support the most interesting feature of the MD simulation, that the hetero-ion pairing is sufficiently strong as to lead to nanometer-scale aggregation of the ions. The presence of such clustering on the nanometer length scale was then confirmed using small-angle neutron scattering experiments. Taken together, the experiment and simulation suggest a molecular-level explanation for the contrasting denaturant properties of guanidinium salts in solution.

Citrate, in Collaboration with a Guanidinium Ion, as a Generator of Cubane-like Complexes with a Range of Metal Cations: Synthesis, Structures, and Magnetic Properties of [C(NH2)3]8[(MII)4(cit)4]·8H2O (M = Mg, Mn, Fe, Co, Ni, and Zn; cit = Citrate)

Aqueous reaction mixtures containing citric acid, guanidinium carbonate, and a range of metal cations (Mg2+, Mn2+, Fe2+, Co2+, Ni2+, and Zn2+) at room temperature give crystalline products of composition [C(NH2)3]8[(M(II))4(cit)4].8H2O (cit = citrate). In all cases, the crystals are suitable for single-crystal X-ray diffraction studies, which reveal that the compounds are isostructural (space group P4(2)/n; a approximately 16.2 A, and c approximately 11.5 A). As was intended, cubane-like [M4(cit)4]8- complex anions are present. The individual citrate units are chiral, but each cubane unit contains two of one hand and two of the other, related around an S4 axis. The cubane units are involved in no less than 40 H-bonding interactions with guanidinium cations and lattice water molecules. Detailed susceptibility and magnetization studies show that the intracluster magnetic coupling within the Mn(II), Fe(II), Co(II), and Ni(II) cubanes is very weak in all cases with J values of -0.82, -0.43, and -0.09 cm(-1) for the Mn, Fe, and Co species, respectively. A two-J model gave the best agreement with the susceptibility and high-field magnetization data for the Ni(II) case, over the whole temperature range studied, and the sign of the parameters, J12 = -0.3 cm(-1) and J13 = +2.97 cm(-1), correlated with the two Ni-(mu3-O)-Ni angles observed in the cluster structure. All members of the 3d-block [M4(cit)4]8- family have spin ground states, ST, of zero, with the higher ST levels just a few reciprocal centimeters away in energy.

Second Half-Reaction of Nitric Oxide Synthase: Computational Insights into the Initial Step and Key Proposed Intermediate

Density functional theory methods have been employed to investigate possible first steps in the second half-reaction of the mechanism of nitric oxide synthases (NOSs). In particular, reactions and complexes formed via transfer of either or both hydrogens of the substrates (NHA) -NHOH group to the Fe-bound O2 were considered. For each of these pathways, the effect of adding an extra electron from tetrahydrobiotperin (H4B) was also examined. The preferred initial pathway involves the simultaneous transfer of both hydrogens of the -NHOH group to the Fe(heme)-O2, without an additional electron, to give the Fe(heme)-HOOH species which lies only marginally higher in energy, 2.5 kcal mol(-1) or less, than the initial bound active site. An alternative mechanism in which only the -NH- proton of the -NHOH group is transferred to the Fe(heme)-O2 to give an Fe(heme)-OOH derivative is found to require only slightly more energy, approximately 2 kcal mol(-1). However, transfer of the proton back to the -NOH nitrogen occurs without a barrier at 298.15 K. Tetrahedral intermediates in which the Fe(heme)-O2 has attached at the guanidinium carbon (C(guan)) of NHA, that is, forms an Fe(heme)-O2-C(guan) link, have also been investigated. All examples of such species considered, that is, with or without hydrogen or electron transfers, lie significantly higher in energy by at least 29.0 kcal mol(-1) than the initial bound active site. Thus, it is suggested that such complexes are not mechanistically feasible. The implications of the present findings for the second half-reaction are also discussed.

Crystal Structures Representing the Michaelis Complex and the Thiouronium Reaction Intermediate of Pseudomonas aeruginosa Arginine Deiminase

L-arginine deiminase (ADI) catalyzes the irreversible hydrolysis of L-arginine to citrulline and ammonia. In a previous report of the structure of apoADI from Pseudomonas aeruginosa, the four residues that form the catalytic motif were identified as Cys406, His278, Asp280, and Asp166. The function of Cys406 in nucleophilic catalysis has been demonstrated by transient kinetic studies. In this study, the structure of the C406A mutant in complex with L-arginine is reported to provide a snapshot of the enzyme.substrate complex. Through the comparison of the structures of apoenzyme and substrate-bound enzyme, a substrate-induced conformational transition, which might play an important role in activity regulation, was discovered. Furthermore, the position of the guanidinium group of the bound substrate relative to the side chains of His278, Asp280, and Asp166 indicated that these residues mediate multiple proton transfers. His278 and Asp280, which are positioned to activate the water nucleophile in the hydrolysis of the S-alkylthiouronium intermediate, were replaced with alanine to stabilize the intermediate for structure determination. The structures determined for the H278A and D280A mutants co-crystallized with L-arginine provide a snapshot of the S-alkylthiouronium adduct formed by attack of Cys406 on the guanidinium carbon of L-arginine followed by the elimination of ammonia. Asp280 and Asp166 engage in ionic interactions with the guanidinium group in the C406A ADI. L-arginine structure and might orient the reaction center and participate in proton transfer. Structure determination of D166A revealed the apoD166A ADI. The collection of structures is interpreted in the context of recent biochemical data to propose a model for ADI substrate recognition and catalysis.

Flame retardance of wood treated with guanidine compounds characterized by thermal degradation behavior

Wood was treated with guanidine phosphate, guanidine carbonate and guanidine nitrate to impart flame retardance. For a study of flame retardance from the standpoint of thermal degradation, the samples were subjected to thermogravimetry (TG) and differential thermal analysis (DTA) to determine if there were any characteristic correlations between thermal degradation behavior and the level of flame retardance. The composition of the chars was studied by the IR spectra to obtain information concerning the thermal degradation mechanism. For the decomposition of samples, the second stage plays a key role in the pyrolysis attributed to flame retardance. When it occurs at lower temperatures (<300 °C), the samples have good fame retardance and when it occurs at higher temperatures (>300 °C), the samples have poor fame retardance.

Structure and Function of Arginases

The arginases catalyze the divalent cation dependent hydrolysis of L-arginine to produce L-ornithine and urea. Although traditionally considered in terms of its role as the final enzyme of the urea cycle, the enzyme is found in a variety of nonhepatic tissues. These findings suggest that the enzyme may have other functions in addition to its role in nitrogen metabolism. High-resolution crystal structures have been determined for recombinant rat liver (type I) arginase and for recombinant human kidney (type II) arginase, their variants, and complexes with products and inhibitors. Each identical subunit of the trimeric enzyme contains an active site that lies at the bottom of a 15 A deep cleft. The 2 essential Mn(II) ions are located at the bottom of this cleft, separated by approximately 3.3 A and bridged by oxygens derived from 2 aspartic acid residues and a solvent-derived hydroxide. This metal bridging hydroxide is proposed to be the nucleophile that attacks the guanidinium carbon of substrate arginine. On the basis of this proposed mechanism, boronic acid inhibitors of the enzyme have been synthesized and characterized kinetically and structurally. These inhibitors display slow-onset inhibition at the pH optimum of the enzyme, and are found as tetrahedral species at the active site, as determined by X-ray diffraction. The potent inhibition of arginases I and II by these compounds has not only delineated key enzyme-substrate interactions, but has also led to a greater understanding of the role of arginase in nonhepatic tissues.

Synthetic, structural, and thermal degradation of a tercopolymer derived from salicylic acid, guanidine, and formaldehyde

A salicylic acid–guanadine–formaldehyde (SGF) tercopolymer was synthesized by the condensation of salicylic acid with guanidine carbonate and formaldehyde in 1 : 1 : 2 molar proportions in the presence of 2M HCl as a catalyst. The SGF tercopolymer was characterized on the basis of elemental analysis and ultraviolet–visible, IR, and NMR spectral studies. The Freeman–Carroll and Sharp–Wentworth methods were used to calculate the activation energy and thermal stability of the tercopolymer. Kinetic parameters such as activation energy, entropy change, free-energy change, frequency factor, apparent entropy change, and order of reaction were calculated with the Freeman–Carroll method. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2278–2283, 2004

Thermal degradation of wood treated with guanidine compounds in air

Wood has been treated with guanidine phosphate, guanidine nitrate, guanidine carbonate and guanidine chloride to impart flame retardancy. The samples were subjected to differential thermal analysis (DTA) and thermogravimetry (TG) from ambient temperature to 800°C in air to study their thermal behaviors. From the resulting data, kinetic parameters for different stages of thermal degradation were obtained following the method of Broido. For the decomposition of wood and flame retardant wood, the activation energy was found to decrease from 116 to 54 kJ mol−1; the char yield was found to increase from 5.6 to 34.9%, LOI from 18 to 41.5, which indicated that the flame retardancy of treated wood was improved. Effects of the different compounds on the degradation and flammability of wood have also been proposed.

Structure-activity relationships of oligoguanidines-influence of counterion, diamine, and average molecular weight on biocidal activities.

A series of different oligomeric guanidines was prepared by polycondensation of guanidinium salts and four different diamines under varying conditions. The antimicrobial activities were evaluated against two to four microorganisms. MALDI-TOF-MS was used to analyze the different oligomers. It was found that in each case three major product type series are dominating. These series are linear and terminated with one guanidine and one amino group (type A), two amino groups (type B), or two guanidine groups (type C), respectively. By using 1,2-bis(2-aminoethoxy)ethane as the amino component, a considerable amount of two additional product series, consisting of cyclic structures, was detected (type D and E). It turned out that an average molecular mass of about 800 Da is necessary for an efficient antimicrobial activity. Lower Mw's result in a rapid decrease of activity. By using guanidinium carbonate as the starting material, oligomers with low biocidal activity were obtained, which was caused by incorporation of urea groups during the polycondensation. The diamine determines the distance between two guanidinium groups. It was shown that both 1,2-bis(2-aminoethoxy)ethane and hexamethylenediamine give oligomers with high biocidal activity. By increasing the chain length of the diamine, the biocidal activity drops again.

Cover Picture: Assembly of Hybrid Organic–Organometallic Materials through Mechanochemical Acid–Base Reactions (Chem. Eur. J. 18/2003)

The cover picture shows schematically the preparation of a crystalline material by grinding (top) of the solid reagents or by crystallization by seeding (bottom) of a solution of the powder obtained from the mechanochemical process. Manual grinding of the organometallic complex [Fe(η5-C5H4COOH)2] with a number of solid bases, namely 1,4-diazabicyclo[2.2.2]octane, 1,4-phenylenediamine, piperazine, trans-1,4-cyclohexanediamine and guanidinium carbonate generates quantitatively the corresponding adducts, [HC6H12N2][Fe(η5-C5H4COOH)(η5-C5H4COO)], [HC6H8N2][Fe(η5-C5H4COOH)(η5-C5H4COO)], [H2C4H10N2][Fe(η5-C5H4COO)2], [H2C6H14N2][Fe(η5-C5H4COO)2] ⋅ 2 H2O and [C(NH2)3]2[Fe(η5-C5H4COO)2]⋅2 H2O, respectively. Crystallization from methanol in the presence of seeds of the ground sample allows to grow single crystals of the adducts, hence determination of the adduct structures by single crystal X-ray diffraction. This, in turn, allows identification and characterization of the polycrystalline materials obtained by the grinding process. These solid-solid processes imply molecular diffusion through the lattice and breaking and reassembling of hydrogen bonded networks and proton transfer from acid to base. For more details see the article by D. Braga, F. Grepioni et al. on p. 4362 ff.

Mono- and Bis-N-[3-(triorganylsilyl)propyl]guanidines and Their Derivatives

Organosilicon guanidine derivatives RNHC(=NH)NHCH2CH2CH2Si(OC2H5)3- n (OH)n [R = H, n = 1; R = (CH2)3Si(OC2H5)3, n = 0] were synthesized by condensation of guanidinium carbonate with (3-aminopropyl)triethoxysilane. The products were brought into ether interchange with thiethanolamine and hydrolytic polycondensation.

2-Amino-4-phenyl-5,6-dihydrobenzo[h]quinazoline

The title compound, C18H15N3, was synthesized by the reaction of 2-phenyl­methyl­idene-3,4-di­hydro­naphthalen-1(2H)-one with guanidine carbonate in ethyl­ene glycol under microwave irradiation. X-ray analysis revealed the formation of a pyrimidine ring. The partially saturated six-membered ring adopts a distorted boat conformation.

Synthesis and crystal structure of [Nd(H2O)2]2(C2O4)3

Some crystals of [Nd(H2O)2]2(C2O4)3 were synthesized hydrothermally by heating at 200°C for 8 days an aqueous suspension of neodymium oxalate decahydrate in presence of terephthallic acid and guanidinium carbonate. They crystallize in the orthorhombic system, space group P212121, with a = 8.6702(7) A, b = 9.558(2) A, and c = 17.009(2) A. The structure of this complex is built up by two independent neodymium atoms, three bischelating oxalate ligands, and four water molecules forming a rectangle building unit of 6-membered ring, [Ln(H2O)2(C2O4)]6. The packing of these units leads to a layer parallel to the plane (001). However, the neodymium atoms of two neighbor layers share an edge of oxalato oxygen atoms thus giving a double-layer. The three dimensionality between these double-layers is insured by hydrogen bonds of water molecules which are bound to the neodymium atoms. There is no “zeolitic water molecule.” The two neodymium atoms are nine-coordinated. In both cases, the coordination polyhedron can be described as a distorted tricapped trigonal prism.

Insights into the reaction mechanism of Escherichia coli agmatinase by site-directed mutagenesis and molecular modelling.

Upon mutation of Asp153 by asparagine, the catalytic activity of agmatinase (agmatine ureohydrolase, EC 3.5.3.11) from Escherichia coli was reduced to about 5% of wild-type activity. Tryptophan emission fluorescence (lambdamax = 340 nm), and CD spectra were nearly identical for wild-type and D153N agmatinases. The Km value for agmatine (1.6 +/- 0.1 mm), as well as the Ki for putrescine inhibition (12 +/- 2 mm) and the interaction of the enzyme with the required metal ion, were also not altered by mutation. Three-dimensional models, generated by homology modelling techniques, indicated that the side chains of Asp153 and Asn153 can perfectly fit in essentially the same position in the active site of E. coli agmatinase. Asp153 is suggested to be involved, by hydrogen bond formation, in the stabilization and orientation of a metal-bound hydroxide for optimal attack on the guanidinium carbon of agmatine. Thus, the disruption of this hydrogen bond is the likely cause of the greately decreased catalytic efficiency of the D153N variant.

Hydrothermal synthesis and structural characterization of Fe(II)-squarate Fe 2(OH) 2(C 4O 4)

Fe 2(OH) 2(C 4O 4) was obtained by hydrothermal synthesis starting from a mixture of FeC 2O 4:H 2C 4O 4:(CN 3H 5) 2,H 2CO 3 (guanidinium carbonate):H 2O in the molar ratio 1:0.5:1.5:200 after a heat treatment at 200 °C for 96 hours. It crystallizes in the monoclinic system, space group P2 1/c with lattice parameters a=3.3500(2) Å, b=10.033(1) Å, c=8.5010(7) Å, β=99.686(5)°, V=281.65(4) Å 3, Z=2. The framework is built up from isolated double chains of [Fe(OH) 3O 3] octahedra sharing edges along the direction [100] and which are connected in the [010] and [001] directions via squarate groups [C 4O 4] 2−: each squarate group being connected to four iron (II)-oxygen double chains.

塩酸グアニジンの吸湿特性に及ぼす添加剤と包装材料の影響

Guanidine hydrochloride, which is known to be effective in the treatment of Lambert-Eaton myasthenic syndrome, is very hygroscopic. Therefore, the mixture of the drug and lactose dispensed at hospital pharmacies tends to easily liquefy even under ordinary storage conditions because of poor compatibility. In this study the physicochemical and chemical stabilities of commercially available guanidine salts, namely hydrochloride, nitrate, carbonate, and sulfate, were investigated at various relative humidity levels. The critical relative humidity of the hydrochloride salt was significantly lower than the others and it was also more hygroscopic than the other three salts, however, nitrate was found to be sufficiently stable regarding humidity. The powder maintained a good flowability after long storage periods. The optimal diluent was selected to use in powders consisting of guanidine hydrochloride in order to stabilize the physicochemical and chemical properties. No solidification or change in appearance were observed in the mixture of the drug and magnesium aluminometasilicate (Neusilin® US2) as diluent and moisture adsorbent. The flow property (angle of repose) of this mixture was also investigated.