Continuous Variation Studies Research Articles

NMR structure of dual site binding of mitoxantrone dimer to opposite grooves of parallel stranded G-quadruplex [d-(TTGGGGT)

The formation of complex between anti-cancer drug mitoxantrone (MTX) and tetra-molecular parallel G-quadruplex DNA [d-(TTGGGGT)]4 has been studied by solution state one and two dimensional NMR spectroscopy. Mitoxantrone forms a head-to-tail dimer and binds at two opposite grooves of the G-quadruplex. The Job's method of continuous variation and thermal melting studies independently ascertain binding stoichiometry of 4:1 in mitoxantrone:DNA complex. The existence of only four guanine NH peaks corresponding to the four G-quartets during the course of titration shows that C4 symmetry of G-quadruplex is intact upon binding of mitoxantrone. The specific inter molecular short distance contacts between protons of two mitoxantrone molecules of dimer, that is, ring A protons with ring C and side chain methylene protons, confirms the formation of mitoxantrone head-to-tail dimer. The observed 38 Nuclear Overhauser Enhancement (NOE) cross peaks between MTX and G-quadruplex DNA indicate formation of a well-defined complex. The three dimensional structure of 4:1 mitoxantrone:[d-(TTGGGGT)]4 complex computed by using experimental distance restraints followed by restrained Molecular Dynamics (rMD) simulations envisages the critical knowledge of specific molecular interactions within ligand-G-quadruplex complex. The findings are of direct interest in development of anti-cancer therapeutic drug based on G-quadruplex stabilization, resulting in telomerase inhibition.

Spectrophotometric study on the charge transfer reaction between 2-amino-4-methylpyridine with chloranilic acid in polar solvents

ABSTRACTCharge transfer (CT) complexes formed between 2-amino-4-methylpyridine as electron donor, chloranilic acid as electron acceptor was investigated spectrophotometrically in acetonitrile (AN), methanol (MeOH) and binary mixture of acetonitrile 50% + methanol 50% (MeOH-AN). Minimum–maximum absorbance method has been used for estimating the formation constants of the CT reactions (KCT). Job’s method of continuous variation and photometric titration studies were used to detect the stoichiometric ratios of the formed complexes, and they showed that 1:1 complexes were produced. The molar extinction coefficient (e), oscillator strength (f), dipole moment (l), CT energy (ECT), ionisation potential (IP) and the dissociation energy (W) of the formed complexes were estimated; they reached acceptable values suggesting the stability of the formed CT complexes. The solid CT complexes were synthesised and characterised by elemental analyses, 1H NMR and FTIR spectroscopies where the formed complexes included proton and electron transfer.

Spectroscopic characterization of charge transfer complexes of 2,3-diaminopyridine with chloranilic acid and dihydroxy-p-benzoquinone in polar solvent

Charge transfer (CT) complexes formed between 2,3-aminopyridine (2,3-DAP) as electron donor with the π-electron acceptors chloranilic acid (CHA) and dihydroxy-p-benzoquinone (DHBQ) were investigated spectrophotometrically in ethanol. Minimum–maximum absorbance method has been used for estimating the formation constants of the charge transfer reactions (KCT). Job’s method of continuous variation and photometric titration studies were used to detect the stoichiometric ratios of the formed complexes and they showed that 1:1 complexes were produced. The molar extinction coefficient (ε), oscillator strength (f), dipole moment (μ), charge transfer energy (ECT), ionization potential (IP) and the dissociation energy (W) of the formed complexes were estimated, they reached acceptable values suggesting the stability of the formed CT-complexes. The solid CT-complexes were synthesized and characterized by elemental analyses, 1H NMR and FTIR spectroscopies where the formed complexes included proton and electron transfer.

Kinetics of N, N-Dimethyaniline-Benzenesulphonylchloride Charge-Transfer Complex Initiated Cyclopolymerization of Divinyl Monomer

Polymerization of non-conjugated divinyl monomer N,N'-methylenebisacrylamide was studied using a novel charge-transfer complex of N,N-dimethylaniline-benzenesulphonyl chloride in a homogeneous gel-free state, under varying conditions of concentration and temperature. The reactions were carried out under various concentrations at a constant temperature of 52 ? in acetonitrile media. The dependence of the rate of polymerization on various experimental conditions, such as different concentrations of monomer N,N'-methylenebisacrylamide, donor N,N-dimethylaniline, acceptor benzenesulphonyl chloride, and temperature were studied. The order with respect to monomer, donor, and acceptor were found to be 1, 0.5, and 0.5 respectively. The kinetic results were interpreted by a suitable mechanistic sequence. Absence of gelation is attributed to the formation of a cyclic polymer. Jobs method of continuous variation studies shows 1:1 complexformation.

LIX ®63 stability in the presence of Versatic 10 under proposed commercial extract and strip conditions, part III: Effect of manganese and cobalt loading on oxime stability at 30 °C

The combination of LIX ®63 with the carboxylic acid Versatic 10 exhibits synergistic properties, enabling direct separation of Co and Zn from Mn, Mg and Ca, a process of interest to the proposed El Boleo copper/cobalt project. Previous work on the chemical stability of this system had revealed the potential for rapid degradation of LIX ®63 oxime (‘oxime’) at high temperature (40, 50 °C) when extracting cobalt and zinc from El Boleo solutions. The present study under extract conditions at 30 °C found increased manganese loading, achieved by increasing operating pH from 4.5 to 6.0, facilitated increased rates of oxime degradation and ‘irreversible’ loading of cobalt. This cobalt was able to be reductively stripped using zinc metal, yielding anti oxime and ‘keto-oxime’. Operation at pH 4.5 resulted in low manganese loading (about 0.2 g/L) and a calculated oxime half life of 67 weeks. Increasing the pH to 6.0 resulted in manganese loading of 2.5 g/L and a decrease in oxime half life to 24 weeks. Operation at pH 6.0 in the absence of manganese gave an oxime half life of 66 weeks. Zinc loading, cobalt loading and changes in pH between 4.5 and 6.0 (excluding the resulting impact on manganese loading) did not appear to have any adverse effect on oxime stability. At a given pH (5.0), ‘irreversible’ Co loading increased with increasing Co concentration in the aqueous solution. This did not have any noticeable effect on oxime half life. The metal:oxime:carboxylic acid stoichiometries of the Zn, Mn and Co synergist complexes were determined by continuous variation and maximum loading studies to be 1:3:2 for all three metals although 1:2:2 remained a possibility for manganese. Inter-conversion of syn oxime to anti oxime was observed to occur via two different mechanisms under the conditions used: a rapid process facilitated by manganese complexation; and a slower, temperature-based isomer re-equilibration process which occurred in the absence of manganese. This inter-conversion process, which resulted in increased manganese and zinc loading occurring relative to fresh organic (cobalt already being fully loaded), also opens up the possibility of decreasing the amount of LIX ®63 required in the El Boleo process.

SYNTHESIS AND CHARACTERIZATION OF TRANSITION METAL COMPLEXES OF 2-THIOACETIC ACID BENZOTHIAZOLE LIGAND

New metal complexes of the ligand 2-thioacetic acid benzothiazole with the metal ions Fe(III), Rh(III), Pd(II), Pt(IV) and Au(III) were prepared in alcoholic medium.The prepared complexes were characterized by FTIR Spectroscopy, electronic spectroscopy, elemental analysis, 1H NMR, 13C NMR, magnetic susceptibility and conductivity measurements. Molar ratio and continuous variation studies in solution gave comparable result with those obtained from solid state study. From the spectral measurements, monomer structures for the complexes were proposed.

Isaindigotone Derivatives: A New Class of Highly Selective Ligands for Telomeric G-Quadruplex DNA

Four isaindigotone derivatives (5a,b and 6a,b) designed as telomeric G-quadruplex ligands have been synthesized and characterized. The unfused aromatic rings in these compounds allow a flexible and adaptive conformation in G-quadruplex recognition. The interaction of human telomeric G-quadruplex DNA with these designed ligands was explored by means of FRET melting, fluorescence titration, CD spectroscopy, continuous variation, and molecular modeling studies. Our results showed that the adaptive scaffold might not only allow the ligands to well occupy the G-quartet but also perfectly bind to the grooves of the G-quadruplex. The synergetic effect of the multiple binding modes might be responsible for the improved binding ability and high selectivity of these ligands toward G-quadruplex over duplex DNA. Long-term exposure of HL60 and CA46 cancer cells to compound 5a showed a remarkable decrease in population growth, cellular senescence phenotype, and shortening of the telomere length, which is consistent with the behavior of an effective telomeric G-quadruplex ligand and telomerase inhibitor.

Synthesis and spectroscopic studies of charge transfer complexes between chloranilic acid and some heterocyclic amines in ethanol

Charge transfer (CT) complexes formed between 2-amino-4-methoxy-6-methyl-pyrimidine (AMMP), 2-amino-4,6-dimethyl-pyrimidine (ADMP), 3-amino-pyrazole (AP), 3,5-dimethyl-pyrazole (DMP), 3-amino-5-methyl-pyrazole (AMP), 2-amino-4-methyl-thiazole (AMT), 2-amino-5-methyl-1,3,4-thiadiazole (AMTD) and 3-amino-5,6-dimethyl-1,2,4-triazine (ADMT) as electron donors with the π-acceptor chloranilic acid (CHA) were investigated spectrophotometrically in ethanol. Minimum–maximum absorbances method has been used for estimating the formation constants of the charge transfer reactions ( K CT). It has been found that K CT depends on the pKa of the studied donors. Job’s method of continuous variation and photometric titration studies were used to detect the stoichiometric ratios of the formed complexes and they showed that 1:1 complexes were produced. The molar extinction coefficient ( ε), oscillator strength ( f), dipole moment ( μ), charge transfer energy ( E CT), ionization potential ( I P) and the dissociation energy ( W) of the formed complexes were estimated, they reached acceptable values suggesting the stability of the formed CT-complexes. The solid CT-complexes were synthesized and characterized by elemental analyses, 1HNMR and FTIR spectroscopies where the formed complexes included proton and electron transfer.

Metal ion interaction with tridentate ONO donor azo ligands : Part I. Equilibrium study on the complex formation of CoII, NiII, CuII and ZnII with azo ligands

The ionization constants of three ONO donor azo ligands (H 2 L 1-3 ) containing different functional groups, viz. 2-hydroxy-2'-carboxy-5-methylazobenzene (H 2 L 1 ), 2,2'-dihydroxyazobenzene (H 2 L 2 ) and 2-hydroxy-2'-hydroxymethyl-5-methylazobenzene (H 2 L 3 ) and their formation constants with M 2+ ions (M = Co, Ni, Cu and Zn) have been determined in dioxane-water (50% v/v) medium at 25 °C at a fixed ionic strength (I = 0.1 mol dm -3 NaNO 3 ) by pH-potentiometric method. The nature of the species present in solution have been elucidated on the basis of their electronic spectra. Job's method of continuous variation study indicated the formation of 1: 1 complex with Cu 2+ ion and 1: 2 complex with Co 2+ and Ni 2+ ions with all these three ligands. Formation constants of these metal ions with all these three ligands have been found to follow the order: Co 2+ Zn 2+ . With respect to any particular metal ion, the formation constant values follow the order: (L 1 ) 2- < (L 2 ) 2- < (L 3 ) 2- which is explained on the basis of overall basicity of these ligands.

Electrometric studies on the system acid-vanadate and the formation of heavy metal vanadates

The stoichiometry of the polyanions formed by the action of nitric acid on sodium ortho-vanadate solution has been studied by means of electrometric techniques involving glass electrode and conductometric titrations as well as Job’s method of continuous variation. The well defined inflections and breaks in the titration curves and maxima from continuous variation study provide cogent evidence for the existence of the anions, pyro-V 2O 7 4−, meta-VO 3 − and poly-H 2V 10O 28 4− corresponding to the ratios of VO 4 3−:H + as 1:1, 1:2 and 1:2.6 in the pH ranges (10.1–10.7), (7.0–7.5) and (3.4–3.8), respectively. Similar titrations between alkali and V 2O 5 solutions also confirm the existence of the same anions. The interaction of lead nitrate with sodium vanadate solutions, at specific pH levels 12.4, 10.5, 7.4 and 3.6 was also studied by pH and conductometric titrations. The end-points obtained from the sharp inflections in the titration curves provide definite evidence for the formation of lead ortho-3PbO·V 2O 5, pyro-2PbO·V 2O 5 and meta-PbO·V 2O 5 vanadates in the vicinity of pH 8.2, 6.5 and 5.6, respectively.

Copper(II) Complexes of Bis(1,4,7-triazacyclononane) Ligands with Polymethylene Bridging Groups: An Equilibrium and Structural Study.

Copper(II) complexation by a series of ligands containing two 1,4,7-triazacyclononane, [9]aneN(3), groups conjoined by polymethylene chains two to six carbons in length is described. Equilibrium modeling studies in aqueous solution using pH-potentiometry indicate that the smallest homologue of the series, EM2, forms only Cu(EM2)(2+) in dilute aqueous solutions. All other ligands of the series form stable 1:1 (protonated and nonprotonated) and 2:1 dicopper(II) (hydroxo and non-hydroxo) complexes. Those ligands that contain bridging chains of four or more carbon atoms likely form dimeric or oligomeric complex species in solution. The EM ligands with the shortest polymethylene bridging groups form the most stable 1:1 species. There is little difference among the ligands (n = 3-6) in complex stability of the protonated, CuH(2)(EMn)(4+), and dicopper(II), Cu(2)(EMn)(4+), species. UV-vis spectroscopic continuous variation studies at pH 4.0 and 7.5 are interpreted on the basis of the principal equilibrium species obtained from the equilibrium models. Single-crystal X-ray diffraction studies on four complexes ([Cu(EM2)]SO(4).6H(2)O (1), [Cu(2)(EM2)Cl(4)].2H(2)O (2), [Cu(2)(EM6)Cl(4) ] (3), and [Cu(EM3)][ZnBr(4)].H(2)O (4)) characterize structural features of several 1:1 monomeric and dicopper(II) complexes in the crystalline solid. The monomeric compounds contain CuN(6) chromophores while the dicopper(II) compounds contain square pyramidal CuN(3)Cl(2) coordination geometry. Compound 1 crystallizes in space group P&onemacr; with a = 7.849(2) Å, b = 9.783(2) Å, c = 16.919(5) Å, alpha = 78.42(3) degrees, beta = 85.76(3) degrees, gamma = 73.06(3) degrees, and Z = 2. 2: P2(1)/n with a = 9.689(3) Å, b = 11.733(3) Å, c = 10.124(3) Å, beta = 98.20(2) degrees, and Z = 2. 3: P2(1)/n with a = 7.278(2) Å, b = 12.416(3) Å, c = 13.781(2) Å, beta = 90.15(2) degrees, and Z = 2. 4: P2(1)/c with a = 9.295(3) Å, b = 16.233(4) Å, c = 16.544(5) Å, beta = 92.62(2) degrees, and Z = 4. Cyclic voltammograms of aqueous solutions prepared by dissolving [Cu(2)(EM2)Cl(4)].2H(2)O confirm its dissociation to Cu(EM2)(2+). Aqueous solutions containing 1:1 molar ratios of Cu(II) and EM2 in 0.1 mol dm(-)(3) KCl at 25 degrees C show a one-electron chemically reversible reduction at scan rates of 500 mV s(-)(1) with E(1/2) (Cu(II)-Cu(I)) = -868 mV relative to SCE. EPR (X- and Q- band) spectra of frozen solutions (1:1 DMSO/H(2)O and glycerol/H(2)O) of Cu(EM2)(2+) at 100 K are typical of axial copper(II) features (X-band parameters: g( parallel) =2.225 (A( parallel) = 164 x 10(-)(4)) and g( perpendicular) = 2.045).

Incorporation of Ru(2)(O(2)C(CH(2))(6)CH(3))(4) into Extended Chains: Interaction of Ru(2)(O(2)C(CH(2))(6)CH(3))(4) with Pyrazine, 4-Cyanopyridine, TCNE, and p-Benzoquinone.

In attempts to form extended chains Ru(2)(O(2)C(CH(2))(6)CH(3))(4) (1) was reacted with both simple coordination and redox-active bridging ligands. The simple coordination ligands, pyrazine (pz) and 4-cyanopyridine (4-cp), coordinated in the axial sites of the diruthenium complex. With the symmetric ligand pyrazine, the polymer [1(pz)](n)() was isolated. With the asymmetric ligand 4-cp, the pyridine nitrogen coordinated preferentially and the bis-adduct 1(4-cp)(2) was isolated. Solution UV/visible and NMR studies indicated that pi-interactions between the Ru-Ru pi and ligand pi orbitals were occurring in both cases. Mole ratio and continuous variation studies of 1 with pyrazine and 4-cp indicated that these axial ligands were labile and that a number of solution species existed. When 1 was reacted with TCNE, redox reactions occurred. Solid-state IR and solution NMR studies also showed that both 1(TCNE) (2) and [1](2)TCNE (3) contained diruthenium carboxylate cores which no longer possessed the D(4)(h)() paddle-wheel geometry. With p-benzoquinone, redox reactions occurred upon coordination to give [1(+)][SQ(-)(*)] (4), which contained an undisrupted oxidized diruthenium tetracarboxylate core. Formation of 4 was reversible in solution, with 1 and p-benzoquinone being favored at higher temperatures.

THE EXTRACTION OF Am(III) FROM NITRIC ACID BY OCTYL(PHENYL)-N,N-DIISOBUTYLCARBAMOYLMETHYLPHOSPHINE OXIDE - TRI-n-BUTYL PHOSPHATE MIXTURES

Abstract The extraction behavior of Am(III) from nitric acid by octy1(phenyl)-N,N-diisobutylcarbamoyl methyphosphine oxides, OØD[IB]CMPO, in the presence of tributylphosphate, TBP, has been studied using diethylbenzene, decalin, and normal aliphatic hydrocarbon diluents. Relative to ØD[IB]CMPO alone, mixtures of TBP and OØD[IB]CMPO show a slight enhancement in the extraction of Am(III) from nitric acid solution above 2 M and a moderate decrease in extraction for lower acid concentrations. The net effect of TBP addition to OØD[IB]CMPO (as well as other selected carbamoyl methylphosphoryl extractants) is a relative insensitivity of the distribution ratio of Am(III) to HNO3 concentration in the range of 0.5 M to 6 M and facilitated stripping of Am(III) with dilute acid. Since a continuous variation study of Am(III) extraction using mixtures of ØOD[IB]CMPO and TBP at a fixed total concentration revealed no evidence of a mixed complex, the TBP appears to be behaving primarily as a phase modifier The most significant benefit gained from addition of TBP to ØD[IB]CMPO is the increased metal ion loading capacity and extractant compatibility with alicyclic and aliphatic diluents. The use of TBP to overcome phase compatibility with other bifunctional extractants of the carbamoylmethylphosphoryl type and the use of other phase modifiers with ØD[IB]CMPO have also been investigated.

A continuous variation study of heats of neutralization

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTA continuous variation study of heats of neutralizationDennis W. Mahoney , Joyce A. Sweeney , Derek A. Davenport , and Richard W. Ramette Cite this: J. Chem. Educ. 1981, 58, 9, 730Publication Date (Print):September 1, 1981Publication History Received3 August 2009Published online1 September 1981Published inissue 1 September 1981https://doi.org/10.1021/ed058p730RIGHTS & PERMISSIONSArticle Views814Altmetric-Citations2LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (2 MB) Get e-Alerts Get e-Alerts

Induction of helicity in polyuridylic acid and polyinosinic acid by silver ions.

AbstractSilver ions binding to poly(U) and poly(I) produce highly ordered multistranded helices under conditions which would otherwise lead to random coils. Evidence for helicity comes from the hypochromicity and high ellipticity generated in the polymers by Ag+ binding, as well as from x‐ray studies and from the cooperativity of the Ag+ complexing reaction. Continuous variation studies show that both polymers form 1:1 and 2:1 polymer–Ag+ complexes. Low pH favors the 1:1 complex with poly(U) and the 2:1 complex with poly(I); the reverse is true at high pH. Ag+ binding and proton‐release experiments make it clear that at low pH, unprotonated electron‐donor groups are complexed preferentially, but that at high pH, Ag+ readily displaces H+ from protonated groups. In poly(I) the unprotonated donor is N(7), leading at low pH to a 2:1 complex containing N(7)‐Ag‐N(7) bonds; at high pH, proton release from N(1) leads to a 1:1 complex containing N(1)‐Ag‐O bonds. In poly(U) there is no unprotonated donor; the low‐pH 1:1 complex involves deprotonation of only one N(3) per bound Ag+, leading to N3‐Ag‐O bonding, while high pH causes deprotonation of two N(3) per Ag+ and a 2:1 N(3)‐Ag‐N(3) complex. Thus silver ions react with the nucleotide bases in chemically predictable ways, and the formation of different Ag–nucleotide bonds leads to different multiple‐helix structures.

The effect of platinum binding on the structure of DNA and its function in RNA synthesis

Summary Circular dichroism titration and continuous variation studies indicate that cis[Pt(NH 3 ) 2 Cl 2 ] forms two complexes with DNA, with 0.1: 1 and 1: 1 Pt/DNA(P) ratios. Trans [Pt(NH 3 ) 2 Cl 2 ] forms only a 1: 2 Pt/DNA(P) complex. The high ellipticity exhibited by the « low-platinumcomplexes is characteristic of the binding of cis Pt, not trans , to native, and not denatured DNA, and involves G-C base pairs, as indicated, for example, by its formation with poly dG.poly dC, but not poly dA.poly dT. Melting curves of 1: 1 trans -Pt-DNA solutions show that the fraction of hypochromicity of uncomplexed DNA that is lost at room temperature by binding to trans Pt is also the fraction of A-T base pairs in the DNA, and the remaining hypochromicity then lost on heating correlates with the G-C content of the DNA. These results indicate Pt crosslinks between G-C bases and denaturation in the A-T rich DNA segments. Cis -Pt-DNA melting is very complex and indicates several different binding modes. RNA polymerase is severely inhibited by the binding of both cis and trans [Pt(NH 3 ) 2 Cl 2 ] to DNA, and the cis isomer inhibits much more strongly. The reaction of either Pt complex with the enzyme has no effect whatever on transcription. The chain length of the RNA produced through the RNA polymerase reaction decreases as the amount of Pt available for DNA binding increases. This effect can be explained by platinum atoms on the DNA template acting to stop chain elongation.

Interaction of metal ions with nucleic acids and related compounds. II. Studies on Au(III)‐nucleic acid system

AbstractThe nature of interaction of Au(III) with nucleic acids was studied by using methods such as uv and ir spectrophotometry, viscometry, pH titrations, and melting‐temperature measurements. Au(III) is found to interact slowly with nucleic acids over a period of several hours. The uv spectra of native calf‐thymus DNA 9pH 5.6 acetate buffer containing (0.01M NaCIO4) showed a shift in λ max to high wavelengths and an increase in optical density at 260 nm. There was a fourfold decrease in viscosity (expressed as ηsp/c). The reaction was faster at pH 4.0 and also with denatured DNA (pH 5.6) and whole yeast RNA (pH 5.6). The order of preference of Au(III) (as deduced from the time of completion of reaction) for the nucleic acids in RNA &gt; denatured DNA &gt; DNA. The reaction was found to be completely reversible with respect KCN. Infrared spectra of DNA‐Au(III) complexes showed binding to both the phosphate and bases of DNA. The same conclusions were also arrived at by melting‐temperature studies of Au(III)‐DNA system. pH titrations showed liberation of two hydroxylions at r = 0.12 [r = moles of HAuCl4 added per mole of DNA‐(P)] and one hydrogen ion at r = 0.5. The probable binding sites could be N(1)/N(7) of adenine, N(7) and/or C(6)O of guanine, N(3) of cytosine and N(3) of thymine.DNAs differing in their (G = C)‐contents [Clostridium perfingens DNA(G = C, 29%), salmon sperm DNA (G + C, 42%) and Micrococcus lysodeikticus DNA(G + C, 29%), salmon sperm DNA (G = C, 72%)] behaved differently toward Au(III). The hyperchromicity observed for DNAs differing in (G + C)‐content and cyanide reversal titrations indicate selectivity toward ( A + T)‐rich DNA at lw values of r. Chemical analysis and job's continuous variation studies indicated the existence of possible complexes above and below r = 1. The results indicate that Au(III) ions probably bind to hte phosphate group in the initial stages of the reaction, particularly at low values of r, and participation of the base interaction also increases. Cross‐linking of the two strands by Au(III) may take place, but a complete collapse of the doulbe helix is not envisaged. It is probable that tilting of the bases or rotaiton of the bases around the glucosidic bond, resulting in a significant distrotion of the double helix, might take place due to binding of Au(III) to DNA.

Spectrophotometric determination of micro amounts of tin(IV) with zephiramine

The thiocyanate complex of tin(IV) reacts with zephiramine to give a white precipitate. The precipitate, extracted into chloroform, has an absorption maximum at 273 nm. The molar absorbancy is about 7500 at 273 nm and is stable for at least 5 hours.The composition for the extracted species is assumed to be 1:4 (Sn:zephiramine) by the continuous variation study. Extraction was carried out with 10 ml of chloroform from 25 ml of the aqueous sample solution. Beer's law holds for the concentration of 5.0×10-6 M to 5.0×10-5 M in the aqueous phase. Micro amounts of tin(IV) can be determined by this method. The effects of diverse ions were investigated, and its result was shown in Table I. Many ions except mercury, copper, iron, cobalt, palladium, platinum, ruthenium, iodate, periodate, vanadate, molybdate and tungstate, do not interfere with the determination when their amounts are equal to that of tin (IV).

Spectrophotometric determination of micro amounts of palladium with zephiramine

The thiocyanate complex of palladium reacts with zephiramine to give brownish yellow precipitate which is extractable into chloroform. The extract has an absorption maximum at 312 mμ. The molar absorbancy is about 3.7×104 and invariable for at least 5 days. The composition of the extracted species was assumed to be 1 : 4 (Pd : zephiramine) by the continuous variation study. The Beer's law held over the range of 2×10-62×10-6M of Pd. Micro amounts of Pd were determined by this method. The effects of numbers of cations and anions were shown.

The stoichiometry of silver chromate and basic copper chromate: Investigations for the freshman laboratory

This project begins with a continuous variation study of the formation of silver chromate and then turns to copper chromate and with this substance the results are unexpected, from beginning to end.