Adsorption, desorption, and surface-promoted hydrolysis of glucose-1-phosphate in aqueous goethite (α-FeOOH) suspensions

Adsorption, desorption, and precipitation reactions at environmental interfaces govern the fate of phosphorus in terrestrial and aquatic environments. Typically, a substantial part of the total pool of phosphorus consists of organophosphate, and in this study we have focused on the interactions between glucose-1-phosphate (G1P) and goethite (α-FeOOH) particles. The adsorption and surface-promoted hydrolysis reactions have been studied at room temperature as a function of pH, time, and total concentration of G1P by means of quantitative batch experiments in combination with infrared spectroscopy. A novel simultaneous infrared and potentiometric titration (SIPT) technique has also been used to study the rates and mechanisms of desorption of the surface complexes. The results have shown that G1P adsorption occurs over a wide pH interval and at pH values above the isoelectric point of goethite (IEP(goethite) = 9.4), indicating a comparatively strong interaction with the particle surfaces. As evidenced by IR spectroscopy, G1P formed pH-dependent surface complexes on goethite, and investigations of both adsorption and desorption processes were consistent with a model including three types of surface complexes. These complexes interact monodentately with surface Fe but differ in hydrogen bonding interactions via the auxiliary oxygens of the phosphate group. The apparent desorption rates were shown to be influenced by reaction pathways that include interconversion of surface species, which highlights the difficulty in determining the intrinsic desorption rates of individual surface complexes. Desorption results have also indicated that the molecular structures of surface complexes and the surface charge are two important determinants of G1P desorption rates. Finally, this study has shown that surface-promoted hydrolysis of G1P by goethite is base-catalyzed but that the extent of hydrolysis was small.     

A stability-indicating HPLC method for the determination of 17β-estradiol-3-phosphate in an ophthalmic solution

Summary Thep-tert-butylcalix[n]arenes (n=4,6,7,8) andp-tert-butyldihomooxacalix[4]arene have been separated by reverse phase liquid chromatography. Optimum conditions have been obtained on a Spherisorb ODS1, 5 m C18 column by isocratic ambient elution with acetonitrile-methyltert-butyl ether. Calibration plots have been obtained from purified calixarenes and the reliability of the method is confirmed from test mixtures of calixarenes of known composition.     

The Lewis basicity of nitrido complexes. Theoretical investigation of the structure and bonding of Cl2 (PH3)3ReN–X (X = BH3, BCl3, BBr3, AlH3, AlCl3, AlBr3, GaH3, GaCl3, GaBr3, O, S, Se, Te)

Quantum chemical calculations using gradient-corrected density functional theory (B3LYP) and ab initio methods at the MP2 level are reported for the geometries and bond energies of the nitrido complexes Cl₂ (PH₃)₃ReN–X (X = BH₃, BCl₃, BBr₃, AlH₃, AlCl₃, AlBr₃, GaH₃, GaCl₃, GaBr₃, O, S, Se, Te). The theoretical geometries are in excellent agreement with experimental values of related complexes which have larger phosphine ligands. The parent nitrido complex Cl₂(PH₃)₃ReN is a very strong Lewis base. The calculated bond dissociation energy of Cl₂(PH₃)₃ReN–AlCl₃ is D _e = 43.7 kcal/mol, which is nearly as high as the bond energy of Me₃N–AlCl₃. The donor-acceptor bonds of the other Cl₂(PH₃)₃ReN–AY₃ complexes are also very strong. Even stronger N–X bonds are predicted for most of the nitrido-chalcogen complexes, which exhibit the trend X = O ≫ S > Se > Te. Analysis of the electronic structure shows that the parent compound Cl₂(PH₃)₃ReN has a Re–N triple bond. The Re–N σ bond is clearly polarized towards nitrogen, while the two π bonds are nearly nonpolar. The Re–N σ and π bonds become more polarized toward nitrogen when a Lewis acid or a chalcogen atom is attached. Bonding in AY₃ complexes should be described as Cl₂(PH₃)₃ReE≡N→AY₃, while the chalcogen complexes should be written with double bonds Cl₂(PH₃)₃Re=N=X. The charge-decomposition analysis indicates that the nitrogen-chalcogen bonds of the heavier chalcogen complexes with X = S, Se, Te can also be interpreted as donor-acceptor bonds between the nitrido complex acting as a Lewis base and the chalcogen atom with an empty p(σ) orbital acting as a Lewis acid. The nitrido oxo complex Cl₂(PH₃)₃ Re=N=O has a covalent N–O double bond. Received: 27 July 1998 / Accepted: 26 October 1998 / Published online: 16 March 1999     

Total Synthesis of Several 3, 3"-Biflavones

BiflavonesareamorecomPlicatedclass0fflavonoids.MostofthemareusefulcomPonentsoftraditionalmedicinetocurediseases.Sincechamaejasminel,anewtoeofbiflavonoidpossessingaC-3/C-3"linkage,wasisolatedfromSteUerachamaejasmaeL.byHuangetal',especiallyafterthebiologicalactivityofani-cancerwasdiscovered',thestUdyof3,3"-biflavonoidshasattfactCdmuchattention.3-5ButtherehasbeennoprogressmentionedonthesynthesisofthiskindofcomPoundsinrecentdecades.AsaresultofoursystematicresearchonthesynthesisofchamaejasInin…     

Synthesis of 3-Phenyl-6-formyl-3, 4-dihydro-2H-1, 3-benzoxazine

Benzoxazine is a novel class of thermosetting resins, which possesses lots of outstanding properties such as no by-products and near-zero shrinkage during polymerization as well as good molecular design flexibility1-2. Furthermore, polybenzoxazines (PBZs)…     

Design,synthesis, and biological evaluation of C1–phosphonamidate analogues of 2-deoxy-d-ribose-1-phosphate

A novel series of phenoxy C1–phosphonamidate derivatives of 2-deoxy-d-ribose have been synthesised as stable analogues of 2-deoxy-α-d-ribose-1-phosphate. A number of synthetic routes were explored for the preparation of these targets. The successful approach involved the synthesis of a protected C1–phosphonate ester 17 via Michaelis–Arbuzov reaction, which was then hydrolysed and coupled with different amino acid esters using aldrithiol. Subsequent hydrogenolysis afforded the targets 2a–g, which were isolated as a mixture of diastereoisomers. The compounds were assayed for inhibition of thymidine phosphorylase (TP) and uridine phosphorylase (UP) and for antiviral and cytostatic activity.     

The Solvent Effect on the Chemoselectivity of Palladium-catalyzed Oligomerization of 3, 3-Dimethyl-l-butyne

The chemoselectivities of PdCl2 and CuCl2-catalyzed oligomerization of 3, 3-dimethyl-butyne: 1, 3, 5-tri-tert-butylbenzene, 2, 2, 7, 7-tetramethyl-3, 6-dichloro-3, 5-octadiene and 2, 2, 7,7- tetramethyl-3, 5-octadiyne were obtained, respectively, by regulating the polarity of the solvent.     

Study on the Interaction of Rare Earth with 3, 5, 3''''-Triiodothyronine

HormoneisaveryhoP0tatkindofbiol0glcalmolede,ltplaTharegulationro1einmetabelism.TheinterachoLofrareeothwithborm0nehasearelybeenreporteds0far[1'2J.lntheprerentwork,theinteraedonofrareearthwith3.5,3'-triiodothryor`ire(T.)wasstodiaibyusingNMRandPOtentiometrictitrationat37tandanionicstrenotofO'15mo1e/LNaC1,TheP0tenhometrictitrah0nwasperformedin1:1DMSO-H.O(vol1imeratio)usingthemethoddedndinprevi01ispeper[3].TheNMR8peaofsarnples(PH=4,to)wererecorded'onBrukerARX-4ooNMRSpeCtrometerusingT…     

Thermodynamical characteristics of the reaction of pyridoxal-5′-phosphate with L-amino acids in aqueous buffer solution

The reaction of pyridoxal-5′-phosphate with L-isomers of alanine, lysine, arginine, aspartic acid, glutamic acid, and glycine in phosphate buffer solution was studied by absorption spectroscopy and the calorimetry of dissolution at physiological acidity of the medium (pH 7.35). The formation constants of Schiff bases during reactions and changes in Gibbs energy, enthalpy, and entropy were determined. It was shown that the formation constant of the Schiff base and its spectral properties depend on the nature of the bound amino acid. The progress of the reaction with a majority of amino acids is governed by the entropy factor due to the predominant role of the dehydration effect of the reaction center of amino acids during chemical reactions. The intramolecular electrostatic interaction of an ionized phosphate group with the positively charged amino group on the end of the chain of amino acid residue stabilizes the Schiff bases formed by lysine and arginine. The extinction coefficient of the base, equilibrium constant, and the exothermic effect of the reaction then increase. The excess negative charge on the end of the chain of amino acid residues of aspartic and glutamic acids destabilizes the molecule of the Schiff base. In this case, the equilibrium constant decreases and the endothermic effect of the reaction increases.     

Solvent dependence of peak frequencies and bandwidths of the ν4 vibration of the series CH3MCl3, M  C,Si, Ge,Sn

The Raman spectra of the carbon—chlorine symmetric stretching mode, ν₄, of the Group IVA methylmetal trichlorides (CH₃MCl₃, M  C, Si, Ge, Sn) were acquired in a number of solvents of varying molecular properties. Non-linear curve fitting procedures were used to separate the four band components resulting from chlorine isotope splitting.The band maxima of the two lighter members of the series were observed to shift to lower frequency with increasing solvent polarizability, indicating the predominance of solute—solvent dispersion forces. In the germanium and tin compounds, on the other hand, the peak frequencies were correlated, instead, with solvent dipole moment. This result is in contrast to earlier studies on the ν₁ (CH₃ symmetric stretching) vibration, for which dispersion interactions are the dominant frequency displacement mechanism in all four compounds.The bandwidths of the ν₄ vibration were found to depend on dipolar interactions in the germanium and tin compounds. However, this correlation was not observed for the two lighter series members, nor for the carbon—chlorine antisymmetric stretching vibration in CH₃SnCl₃.     

η3-Propargyl complexes of molybdenum, tungsten, and rhenium

The reactions of the Me _n C₆H_6−n M(CO)₃ (M=Cr, Mo, W;n=3, 5, 6) and C₅R₅M(CO)₃ (M=Mn, Re; R=H, Me) complexes with propargyl alcohol in acidic media under UV irradiation were studied. Novel Me _n C₆H_6−n M(CO)₂(η³-C₃H₃)BF₄ (M=Mo, W;n=3, 5, 6) and C₅R₅Re(CO)₂(η³-C₃H₃)CF₃SO₃ complexes with the 3ē-propargyl ligand were synthesized, and their properties compared with those of similar η³-allyl derivatives. The structure and dynamic propeties of the compounds obtained are discussed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1796–1803, September, 1999.     

Molecular and Crystal Structure of 2, 3, 5, 6-dipropylene-r-pyrone

11NTRODUCT1ONWeattemptedtosynthesizeanextractant(1)bythereactionofadipylchloridewithcyclopentanonepiperidineenamineaccordingtoHunig'sprocedure"',however,wemainlyobtainedthetitlecompound,whichmaybepossiblyapotentialmedicinet2'3i.Itsmolecularstructurewasfinallyconfirmedbythesingle-crystalstructuredeterminationafterconventionalUV,IR,lHNMR,MSandelementana-lyticalworks.2EXPER1MENTALSECT1ON2.1SynthesisToastirredsolutioncontaining8Omlofchloroform,2.8mloftri-ethylamineand1.51g(O-Olmol)…     

Structural and bonding aspects of molybdenum tricarbonyl complexes of 2,4,6-tritertiarybutyl-1,3,5-triphosphabenzene,P3C3But3 and some λ3,λ3,λ5- and λ3,λ5,λ5-alkylated derivatives

The molecular structure of the previously reported compound [Mo(CO)₃(η⁶-P₃C₃Bu^t₃)] has been determined by a single-crystal X-ray diffraction study. Syntheses and molecular structures are also described for the structurally related compounds [Mo(CO)₃(η⁵-P₃C₃Bu^t₃)(Me)(Buⁿ)], [Mo(CO)₃(η⁵-P₃C₃Bu^t₃)(H)(Buⁿ)] and [Mo(CO)₃(η⁴-P₃C₃Bu^t₃(Me)(Buⁿ)(H)(O)Li(THF)₃]. Density functional calculations at the B3LYP/cc-pVDZ(-PP) and BP86/cc-pVDZ(-PP) levels have been carried out on the above complexes and the nature of the bonding between the different rings and molybdenum is discussed. ³¹P NMR spectroscopic evidence is presented for the existence of the novel complex [Mo(CO)₃(η⁶-P₃C₃Bu^t₃)PtCl₂(PEt₃)] in which the triphosphabenzene ring acts as an overall 8-electron donor to the two metal centres.     

Chemical transformations of pyridoxal and pyridoxal 5′-phosphate condensation products with amino acids

The mechanism of chemical transformations of pyridoxal and pyridoxal 5′-phosphate condensation products with amino acids is studied by kinetic measurements. The Schiff bases are shown to be fairly stable in neutral media. In acid media, the Schiff bases are hydrolyzed into the initial components. In alkaline media, cleavage of α-hydrogen from the amino acid fragment and structural rearrangement into the quinoid form followed by hydrolysis of the latter with elimination of pyridoxamine and keto acid take place. The rate constants of the chemical transformations of the Schiff bases are found to depend on the pH of the medium. It is shown for the first time that the phosphate group in the pyridoxal 5′-phosphate fragment catalyzes the α-hydrogen cleavage and strongly accelerates alkaline decomposition of the Schiff bases.     

Synthesis of 6-chloronicotinates of steroidal 3β,5α,6β-triols and 3β,5-dihydroxy-6-ketones

New esters of 3β,5α,6β-trihydroxysteroids and 3β,5-dihydroxy-6-ketosteroids containing 6-chloropyridine groups characteristic of the alkaloid epibatidine were synthesized by acylation with 6-chloronicotinoylchloride. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 175-179, March-April, 2009.     

Effect of BaNH,CaNH,Mg3N2 on the activity of Co in NH3 decomposition catalysis

Development of active and non-noble metal-based catalyst for H2 production via NH3 decomposition is crucial for the implementation of NH3 as a H2 carrier.Co-based catalysts have received increasing attention because of its high intrinsic activity and moderate cost.In this work,we examined the effect of BaNH,CaNH and Mg3 N2 on the catalytic activity of Co in the NH3 decomposition reaction.The H2 formation rate ranks the order as Co-BaNH>Co-CaNH>Co-Mg3 N2≈Co/CNTs within a reaction temperature range of 300-550℃.It is worth pointing out that the H2 formation rate of Co-BaNH at 500℃reaches20 mmolH2 gcat-1 min-1,which is comparable to those of the active Ru/Al2 O3(ca.17 mmolH2 gcat-1 min1)and Ru/AC(21 mmolH2 gcat-1 min-1)catalysts under the similar reaction conditions.In-depth research shows that Co-BaNH exhibits an obviously higher intrinsic activity and much lower Ea(46.2 kJ mol-1)than other Co-based catalysts,suggesting that BaNH may play a different role from CaNH,Mg3 N2 and CNTs during the catalytic process.Combined results of XRD,Ar-TPD and XAS show that a[Co-N-Ba]-like intermediate species is likely formed at the interface of Co metal and BaNH,which may lead to a more energy-efficient reaction pathway than that of neat Co metal for NH3 decomposition.     

Synthesis and properties of monoimines of α-diketones, derivatives of 3-imidazoline nitroxides

The reaction of 4-(2R-1-chloro-2-oxoethylidene)-substituted imidazolidine-1-oxyl with sodium azide gives monoimines of -diketones, derivatives of 3-imidazoline nitroxides. Reactions of these products with nitrogen binucleophiles were used to prepare various heterocyclic compounds containing an imidazoline nitroxide moiety.