Competitive adsorption behavior of heavy metals on kaolinite

Polluted and contaminated soils can often contain more than one heavy metal species. It is possible that the behavior of a particular metal species in a soil system will be affected by the presence of other metals. In this study we have investigated the adsorption of Cd(II), Cu(II), Pb(II), and Zn(II) onto kaolinite in single- and multi-element systems as a function of pH and concentration, in a background solution of 0.01 M NaNO3. In adsorption edge experiments, the pH was varied from 3.5 to 10.0 with total metal concentration 133.3 microM in the single-element system and 33.3 microM each of Cd(II), Cu(II), Pb(II), and Zn(II) in the multi-element system. The value of pH50 (the pH at which 50% adsorption occurs) was found to follow the sequence Cu相似文献   

A versatile microfabricated platform for electrophoresis of double- and single-stranded DNA

We demonstrate a versatile microfabricated electrophoresis platform, incorporating arrays of integrated on-chip electrodes, heaters, and temperature sensors. This design allows a range of different sieving gels to be used within the same device to perform separations involving both single- and double-stranded DNA over distances on the order of 1 cm. We use this device to compare linear and cross-linked polyacrylamide, agarose, and thermo-reversible Pluronic-F127 gels on the basis of gel casting ease, reusability, and overall separation performance using a 100 base pair double-stranded DNA ladder as a standard sample. While cross-linked polyacrylamide matrices provide consistently high-quality separations in our system over a wide range of DNA fragment sizes, Pluronic gels also offer compelling advantages in terms of the ability to remove and reload the gel. Agarose gels offer good separation performance, however, additional care must be exercised to ensure consistent gel properties as a consequence of the need for elevated gel loading temperatures. We also demonstrate the use of denaturing cross-linked polyacrylamide gels at concentrations up to 19% to separate single-stranded DNA fragments ranging in size from 18 to 400 bases in length. Primers differing by 4 bases at a read length of 30 bases can be separated with a resolution of 0.9-1.0 in under 20 min. This level of performance is sufficient to conduct a variety of genotyping assays including the rapid detection of single nucleotide polymorphisms (SNPs) in a microfabricated platform. The ability to use a single microelectrophoresis system to satisfy a wide range of separation applications offers molecular biologists an unprecedented level of flexibility in a portable and inexpensive format.     

Thiotropolone as a chromogenic reagent for the simultaneous determination of cobalt(II) and nickel(II)

Thiotropolone forms chloroform-soluble reddish-brown and violet complexes with cobalt(II) and nickel(II), in the pH range 7.0-8.5 and 6.0-9.0 respectively. Based on this, a sensitive and rapid method for the spectrophotometric determination of traces of cobalt and nickel in metals and alloys has been developed. The two metals can be determined accurately in the range 0.6-2.6 ppm of cobalt and 0.75-4.57 ppm of nickel, simultaneously.     

Nucleophilic substitution in certain bicyclic sesquiterpene alcohols under chemical lonization conditions

Substitution of amino for hydroxyl groups in certain sesquiterpene alcohols has been studied by chemical ionization mass spectrometry using ammonia and ammouia-d₃ as the reagent gases, and by mass-analysed ion kinetic energy spectrometry and collision-induced decomposition mass-analysed ion kinetic energy measurements. Depending upon the source conditions and the nature of the substrates, both S_Ni and S_N1 mechanisms have been found to operate. No evidence is obtained for an S_N2 mechanism in these compounds. In centdarol and isocentdarol, addition of NH₃ to the double bond, followed by elimination of H₂O, also contributes to the substitution process. Attack of [NH₄]⁺ on the epoxide function, followed by loss of H₂O, appears to lead to the substitution ions in epoxycentdarol, epoxyisocentdarol and epoxyhimachalol.     

Halogen oxidation and nitrosylation of some aldimine and ketimine carbonyl complexes of chromium and molybdenum

Summary The halogen oxidation and nitrosylation of cis-[(SB)M-(CO)₄] [M = Cr or Mo, SB = N,N-ethylenebis(p-tolualideneimine), N,N-ethylenebis(p-N,N-dimethylaminobenzalideneimine) or N,N-ethylenebis(methyl-p-methoxyphenylketimine); M = Mo, SB = N,N-ethylenebis-(cinnamylideneimine) or N,N-ethylenebis(methyl-p-methylphenylketimine)] have been studied. Halogenation of [(SB)Cr(CO)₄] yielded [(SB)CrX₂] (X = Cl, Br or I) where-as [(SB)Mo(CO)₄] gave [(SB)Mo(CO)₃X₂] (X = Br or I) and [(SB)MoX _x ] (X = I, n = 2; X = Cl or Br, n = 4). NOCl produced [(SB)Cr(NO)₂Cl₂] and [(SB)Mo(CO)₂(NO)Cl] when reacted with the corresponding [(SB)M(CO)₄]. The complexes were characterized by physico-chemical and spectroscopic measurements.     

Preparation of the first examples of ansa-spiro substituted fluorophosphazenes and their structural studies: analysis of C-H...F-P weak interactions in substituted fluorophosphazenes

The reactions of fluorophosphazenes, endo ansa FcCH(2)P(S)(CH(2)O)(2)[P(F)N](2)(F(2)PN) (1) (Fc = ferrocenyl) and spiro [RCH(2)P(S)(CH(2)O)(2)PN](F(2)PN)(2) (R = Fc (2), C(6)H(5) (3)], with dilithiated diols have been explored. The study resulted in the formation of the first examples of ansa-spiro substituted fluorinated cyclophosphazenes as well as a bisansa substituted fluorophosphazene. The bisansa compound [1,3-[FcCH(2)P(S)(CH(2)O)(2)]][1,5-[CH(2)(CH(2)O)(2)]]N(3)P(3)F(2) (4) was found to be nongeminaly substituted with both the ansa rings in cis configuration, which is in stark contrast to the observations on cyclic chlorophosphazenes where geminal bisansa formation has been observed. The ansa-spiro compounds (5-7) underwent the ansa to spiro transformation leading to dispiro compounds in the presence of catalytic amounts of CsF at room temperature. Two of the ansa-spiro compounds, endo-[3,5-[FcCH(2)P(S)(CH(2)O)(2)]][1,1-[CH(2)(CH(2)O)(2)]]N(3)P(3)F(2) (5) and endo-[3,5-[FcCH(2)P(S)(CH(2)O)(2)]][1,1-[FcCH(2)P(S)(CH(2)O)(2)]]N(3)P(3)F(2) (6), were structurally characterized, and the crystal structures indicate boat-chair conformation as well as crown conformation for the eight-membered ansa rings. Weak C-H.F-P interactions observed in the crystal structures of the ansa-spiro substituted fluorophosphazene derivatives have been analyzed and compared with C-H.F-P interactions of other fluorinated phosphazenes and thionyl phosphazenes.     

Chloro(η6‐p‐cymene)(phosphoramidite)ruthenium(II), a 16‐Electron Fragment Stabilized by an η2‐Aryl–Metal Interaction,and Its Use in Asymmetric Cyclopropanation

Chloride abstraction from the half‐sandwich complexes [RuCl₂(η⁶‐p‐cymene)(P*‐κP)] ( 2a : P* = (S_a,R,R)‐ 1a = (1S_a)‐[1,1′‐binaphthalene]‐2,2′‐diyl bis[(1R)‐1‐phenylethyl)]phosphoramidite; 2b : P* = (S_a,R,R)‐ 1b = (1S_a)‐[1,1′‐binaphthalene]‐2,2′‐diyl bis[(1R)‐(1‐(1‐naphthalen‐1‐yl)ethyl]phosphoramidite) with (Et₃O)[PF₆] or Tl[PF₆] gives the cationic, 18‐electron complexes dichloro(η⁶‐p‐cymene){(1S_a)‐[1,1′‐binaphthalene]‐2,2′‐diyl {(1R)‐1‐[(1,2‐η)‐phenyl]ethyl}[(1R)‐1‐phenylethyl]phosphoramidite‐κP}ruthenium(II) hexafluorophosphate ( 3a ) and [Ru(S)]‐dichloro(η⁶‐p‐cymene){(1S_a)‐[1,1′‐binaphthalene]‐2,2′‐diyl {(1R)‐1‐[(1,2‐η)‐naphthalen‐1‐yl]ethyl}[(1R)‐1‐(naphthalen‐1‐yl)ethyl]phosphoramidite‐κP)ruthenium(II) hexafluorophosphate ( 3b ), which feature the η²‐coordination of one aryl substituent of the phosphoramidite ligand, as indicated by ¹H‐, ¹³C‐, and ³¹P‐NMR spectroscopy and confirmed by an X‐ray study of 3b . Additionally, the dissociation of p‐cymene from 2a and 3a gives dichloro{(1S_a)‐[1,1′‐binaphthalene]‐2,2′‐diyl [(1R)‐(1‐(η⁶‐phenyl)ethyl][(1R)‐1‐phenylethyl]phosphoramidite‐κP)ruthenium(II) ( 4a ) and di‐μ‐chlorobis{(1S_a)‐[1,1′‐binaphthalene]‐2,2′‐diyl [(1R)‐1‐(η⁶‐phenyl)ethyl][(1R)‐1‐phenylethyl]phosphoramidite‐κP}diruthenium(II) bis(hexafluorophosphate) ( 5a ), respectively, in which one phenyl group of the N‐substituents is η⁶‐coordinated to the Ru‐center. Complexes 3a and 3b catalyze the asymmetric cyclopropanation of α‐methylstyrene with ethyl diazoacetate with up to 86 and 87% ee for the cis‐ and the trans‐isomers, respectively.     

Molecular orbital studies on the structure of nucleoside analogs. IV. Conformation of 3-deazapurine nucleosides

Conformational properties of 3-deazapurine nucleosides (namely, 3-deazaadenosine and 3-deazaguanosine) have been investigated by the PCILO method. Both C(2′)-endo and C(3′)-endo sugar puckers have been considered and the results indicate that the conformational preferences of these nucleoside analogs are quite different from those of their parent nucleosides adenosine and guanosine, respectively. This result has been correlated in terms of the biological inactivity of these nucleoside analogs.     

Complexometric titration of copper(II) using nitrosochromotropic acid as a new metal indicator

Summary Nitrosochromotropic acid gives a violet coloured soluble complex with Cu^II in ammonium chloride-ammonium hydroxide buffer solution, which is less stable than Cu^II-EDTA complex. When microquantities of Cu^II solution containing 1 or 2 drops of nitrosochromotropic acid in the ph range 7.25 to 8.00, are titrated with EDTA, a sharp colour change from violet to orange occurs at the end point. The method of titration can be carried out from 20° to 40° C, but the copper complex dissociates at higher temperature and gives low results. The separation of Zn²⁺, Cd²⁺, Co²⁺, Ni²⁺, Pb²⁺ and alkaline earths, is necessary as they interfere in the titrations with EDTA.

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Zusammenfassung Nitrosochromotropsäure bildet mit Kupfer(II) in Ammoniumchlorid-Ammoniak-Pufferlösung einen violett gefärbten löslichen Komplex, der weniger stabil ist als der Kupfer(II)-ÄDTA-Komplex. Mikromengen Kupfer(II) können imph-Bereich von 7,25–8,00 unter Zusatz von 1–2 Tropfen Nitrosochromotropsäurelösung als Indicator mit ÄDTA-Lösung titriert werden, wobei am Endpunkt ein scharfer Umschlag von Violett nach Orange erfolgt. Die Temperatur der Lösung soll 20–40° C betragen; bei höherer Temperatur erhält man zu niedrige Werte, da der Kupferkomplex dann dissoziiert. Zn²⁺, Cd²⁺, Co²⁺, Ni²⁺, Pb²⁺ und Erdalkalien müssen vor der Titration abgetrennt werden.

     

Conformation of nucleoside antibiotics

Minor modifications or substitutions in the sugar or in the base part of pyrimidine and purine nucleosides have a profound effect on their biological activity. These modified nucleosides usually become antiviral, antibacterial, or cancerostatic agents and they are collectively called nucleoside antibiotics. The conformational properties of some of these nucleoside antibiotics have been studied by the PCILO method. The results obtained from such study indicate that the conformational preferences of these nucleoside antibiotics are very similar to those of their parent nucleosides and especially so in the situations that occur in aqueous solutions. The important biological significance of these results is that these nucleoside antibiotics can easily get incorporated into growing chains of DNA and RNA by mimicking their parent nucleosides and can interfere with the protein synthesis of RNA or DNA synthesis.