Abrupt CO2 release to the atmosphere under glacial and early interglacial climate conditions.

Pulse-like carbon dioxide release to the atmosphere on centennial time scales has only been identified for the most recent glacial and deglacial periods and is thought to be absent during warmer climate conditions. Here, we present a high-resolution carbon dioxide record from 330,000 to 450,000 years before present, revealing pronounced carbon dioxide jumps (CDJ) under cold and warm climate conditions. CDJ come in two varieties that we attribute to invigoration or weakening of the Atlantic meridional overturning circulation (AMOC) and associated northward and southward shifts of the intertropical convergence zone, respectively. We find that CDJ are pervasive features of the carbon cycle that can occur during interglacial climate conditions if land ice masses are sufficiently extended to be able to disturb the AMOC by freshwater input.

Some new chromogens for iron, cobalt, and copper Substituted hydrazidines and 1,2,4-triazines containing the ferroin group.

The spectral characteristics and solution conditions requisite for formation of the iron(II), cobalt(II), and copper(I) complexes of some newly synthesised compounds containing the ferroin functional grouping have been determined. These properties are useful for evaluation of the possible analytical effectiveness of the compounds as spectrophotometric reagents for the determination of iron, cobalt, and copper.

Metal-ion chromatography on silica-immobilized 2-pyridinecarboxyaldehyde phenylhydrazone.

The chromatographic properties of silica-immobilized 2-pyridinecarboxyaldehyde phenylhydrazone as stationary phase for separation of aqueous metal-ion mixtures containing various combinations of Mn(II), Fe(II), Cd(II), Zn(II), Co(II), Pb(II), and Cu(II) are described. Separations were achieved in many cases by using mobile phases containing chloride or perchlorate anions, at moderate flow-rates. Quantitative chromatographic analysis was possible for a variety of sample types over a wide range of metal-ion concentrations.

Separation of some transition-metal ions on silica-immobilized 2-pyridinecarboxaldehyde phenylhydrazone.

A metal-ion extractant, prepared by chemical binding of 2-pyridinecarboxaldehyde phenylhydrazone on a silica support, is described and shown to be effective for use in separation and determination of trace amounts of iron, cobalt, nickel, and copper. Metal-ion sorption conforms to the Langmuir isotherm. The relative orders of the Langmuir constants K and the column retention-capacity factors k' for the four transition-metal ions are the same as the natural order of the stabilities predicted for their metal chelates: Fe(II) < Co(II) < Ni(II) < Cu(II).

New chromogens of the ferroin type-X synthesis and chelation properties of some 2-thiazolyl- and 2-pyrimidinylhydrazones.

Preparation of some new hydrazones which possess the ferroin chromophoric group is described, together with results of spectrophotometric studies of their chelation reactions with iron(II), copper(I), cobalt(II) and nickel(II). Several of the new compounds show promise as highly sensitive chromogenic reagents for simultaneous determinations of these metals.

Investigation of selected ferroin-type compounds as fluorometric reagents Determination of zinc with 2-(4-methyl-2-pyridyl)-5(6)-phenylbenzimidazole.

In a search for new fluorometric reagents for trace metal determinations, forty different ferroin-type compounds and their silver, lead and zinc chelates were tested for luminescence in aqueous-ethanol solutions at various pH values. Twelve formed fluorescent chelates of potential analytical utility, and the results revealed some correlation between ligand structure and fluorescence. After identification of the most sensitive fluorometric reagent for zinc among those tested, a spectrophotofluorometric method for the determination of zinc was developed. Proper control of pH and reagent concentration allows determination of nanogram amounts of zinc.

Synthesis and chromogenic properties of some hydrazones of 3-isoquinolyl-, 2-quinolyl- and 2-pyrrole-carbaldehydes.

Preparation of some new hydrazones is described together with results of spectrophotometric studies of their chromogenic reactions with some first-row transition metal(II) ions. Several of the new compounds show promise as highly sensitive metallochromic reagents.

New colorimetric reagents for determination of trace amounts of oxidants and reductants.

The mixed-ligand complexes H[Fe(phen)(CN)(4)] and K(2)[Fe(phen)(CN)(4)] (where phen represents 1,10-phenanthroline) have been found useful as colorimetric reagents for trace determination of reductants and oxidants. Their properties and some representative applications are described.

New chromogens of the ferroin-type-I. Substituted triazines related to 6-cyano-2,2'-bipyridine.

A spectrophotometric study has been made of the iron(II), cobalt(II), nickel(II) and copper(I) chelates of seven new compounds that contain the ferroin functional grouping. None of the new compounds proved to be superior to chromogenic reagents currently in use, but the results are of interest in designing new chromogens.

New chromogens of the ferroin-type--II. Pyrido and pyridyl derivatives of phenazine and quinoxaline.

Eleven pyrido and pyridyl derivatives of phenazine (6) and quinoxaline (5) have been examined as chromogens of the ferroin type for iron(II) and copper(I). Three of the quinoxaline derivatives show promise as reagents for iron(II) but are expensive and difficult to prepare.

New chromogens of the ferroin type--III: some 2-substituted benzimidazole derivatives.

A spectrophotometric study has been made of the iron(II) and copper(I) chelates of 23 new compounds that contain the ferroin functional grouping. Although none of the compounds proved to be superior to chromogenic reagents currently in use, the results are of interest from the point of view of designing new chromogens for iron and copper.

New chromogens of the ferroin-type-IV Oximes of substituted methyl and phenyl 2-pyridyl ketones.

The spectral characteristics, and solution conditions requisite for formation, of the iron(II), cobalt(II), and copper(I) chelates of some newly synthesized oximes containing the ferroin functional grouping have been determined. For some of the oximes, both syn- and anti-isomers were available for study. NMR spectra of the isomers differed, enabling structural distinctions to be made. None of the anti-isomers formed coloured metal chelates. A practical method for distinguishing between the isomers can be based on these findings. Two of the compounds proved very promising as highly sensitive chromogens for determining iron in strongly alkaline materials.

New chromogens of the ferroin type-V Pyridylpyrimidines, bidiazines and other substituted derivatives of diazines.

Spectrophotometric studies of the reactions of iron(II), copper(I) and cobalt(II) with 33 new compounds have demonstrated that the chromogenic properties of diazyl groups are inferior to those of triazyl or pyridyl groups when incorporated into the ferroin chromophore group. The metal complexes of the diazyl derivatives are less stable than those of the corresponding pyridyl and triazyl derivatives. Conditional formation constants of the iron(II) chelates of some representative diazyl derivatives indicate that pyridazyl groups impart greater stabilities than pyrimidyl or pyrazyl groups. Five of the new chromogens have structures that suggest they can chelate iron(II) without steric hindrance, either as bidentate or as terdenate ligands. Although the terdentate mode would ordinarily be expected, two of the five were found to act preferably as bidentate ligands.

Spectrophotometric determination of copper in alkaline solutions and evaluation of some hydroxy-substituted 1,10-phenanthrolines as chromogenic reagents.

Seven new hydroxy-substituted 1,10-phenanthroline derivatives have been evaluated as chromogenic reagents for the determination of copper in strongly alkaline solution. The most sensitive of these, 2,9-dimethyl-4,7-dihydroxy-1,10-phenanthroline, has proven to be highly effective in a simple, rapid procedure for determining trace amounts of copper in sodium hydroxide, potassium carbonate, sodium phosphate or ammonium hydroxide.

Spectrophotometric determination of iron and reducing agents with PPTS, a new water-soluble ferroin-type chromogen of superior sensitivity.

A sulphonated derivative of 3-(4-phenyl-2-pyridyl)-5-phenyl-1,2,4-triazine has been prepared, its structure identified, and its chelation products with iron(II) and copper(I) identified and characterized. The water-soluble compound, referred to as PPTS, has been applied to the determination of iron in various types of samples and the spectrophotometric determination of trace quantities of certain reductants.

Synthesis of certain pyridinyl and diazinyl hydrazones containing one or more ferroin groups, and their chromogenic reactions with iron, copper, cobalt and nickel.

Fifteen new hydrazones with one or more ferroin groups were prepared, and their chelation and chromogenic properties with iron(II), copper(I), cobalt(II) and nickel(II) were investigated. Improved sensitivity in the spectrophotometric determination of cobalt, copper, and nickel is provided by several of the new compounds. Several others are capable of forming unusually stable and interesting binuclear iron(II) complexes.

Synthesis and evaluation of some pyridyl-substituted pyrimidines as copper-specific chromogenic reagents.

Preparation and metal-ion chromogenic properties of five new 2,4,6-trisubstituted pyrimidines containing pyridyl and methyl or phenyl groups are described. All five exhibit specific chromogenic reactions with copper(I), and two possess suitable characteristics for use as sensitive spectrophotometric copper reagents. The results obtained are also of interest in designing related chromogenic reagents.

Synthesis and metallochromic properties of some hydrazones of 2-, 3- and 8-hydrazinoquinoline.

Twenty-two new hydrazones were synthesized for evaluation as possible calorimetric reagents for trace determinations of iron, cobalt, nickel, copper and zinc. Spectrophotometric studies revealed that several show promise as sensitive reagents, with possible utility for simultaneous determinations of two or more of the metals. Conclusions regarding geometric structures of some of the hydrazones and chelates were deduced from mole-ratio studies.

New chromogens of the ferroin type-IX 2-pyridyl and pyrazinylhydrazones of some pyridyl, pyrazinyl and pyridazinyl ketones and of isatin and phenylglyoxal.

Chromogenic properties of 22 new hydrazones, all ferroin-type compounds, have been evaluated with respect to iron(II), copper(I), cobalt(II) and nickel(II). Some show promise as sensitive reagents for the determination of trace amounts of these metal ions. Stoichiometric ratios were determined for the iron(II) chelates and interpreted to distinguish between syn- and anti-isomers.

New chromogens of the ferroin type-VII Some 3-substituted-1,2,4-triazines, 3,5-disubstituted-1,2,4-triazolines and triazoles, and 2,4- and 2,6-bis triazinyl and triazolinyl substituted pyridines.

Chelation and chromogenic properties of 39 new ferroin compounds in reactions with iron(II), copper(I), and cobalt(II) have been investigated spectrophotometrically. The results demonstrate that the chromogenic properties of triazole and triazoline heterocycles are inferior to triazine and pyridine when incorporated into the ferroin chromophore grouping. The triazole and triazoline compounds also undergo hydrolytic decomposition, strongly catalysed by iron(II), making them unsuitable as colorimetric reagents. An outstanding chromogen was found from among the triazine derivatives which is superior in sensitivity to all ferroin-type chromogens previously studied.