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The difference between the values of 4-carboxyphenyl groups, covalently attached to either graphite (BAcarbon) or glassy carbon (BA-GC) surfaces, and benzoic acid in solution is explored using potentiometric titration and cyclic voltammetry. In solution, benzoic acid has a pKa of 4.20 at 25 degrees C. However, the observed pKa value on the graphitic surfaces shows significant deviations, with BAcarbon exhibiting a large shift to higher pKa values (pKa = 6.45) in contrast to BA-GC, which is shifted to lower pKa values (pKa = 3.25). Potentiometric titrations at temperatures between 25 and 50 degrees C allowed us to determine the surface pKa of these materials at each temperature studied and hence to determine the enthalpy, entropy, and Gibbs' energy changes associated with the ionization of the carboxylic acid groups. It was found that the enthalpic contribution is negligible and that the changes in surface pKa values are entropically controlled. This suggests that solvent ordering/disordering around the interface strongly influences the observed pKa value, which then reflects the relative hydrophobicity/hydrophilicity of the different graphitic surfaces.

4-Nitrophenol (4-NP)or 4-nitrobenzyl alcohol (4-NBA) are used as voltammetric and X-ray photoelectron spectroscopic (XPS) labels for carboxylic acid groups on the surface of single-walled carbon nanotubes, bamboo-like" and hollow-tube" multi-walled carbon nanotubes. The surface carboxyl groups are first converted to the corresponding acyl chlorides, and coupled to the labels via the formation of an ester linkage. The voltammetric reduction of the arylnitro label allows the number of carboxyl groups on the surface to be estimated. Alternatively the percentage of the elemental surface composition corresponding to the carboxyl groups can be measured using XPS via the emission from the N1s level of the label. The number of electroactive quinonyl groups present on the surface relative to the number of carboxyl groups can also be determined voltammetrically by measuring the area under the voltammetric wave corresponding to the surface quinone groups. By combining these voltammetric and XPS results the relative percentages of the O1s spectral peak, which correspond to carboxyl and quinonyl groups, can then be determined, which also allows, by difference, an estimate of the percentage elemental surface composition of total other oxygen-containing functionalities present such as lactones, ethers, aliphatic ketones etc. The effect of standard acid pre-treatments used to introduce carboxyl groups onto the CNT surface (such as stirring in relatively concentrated mixtures of nitric and sulfuric acids) on the number of each type of oxygen functionality is compared. In all cases the number of carboxyl groups is found to increase, but the number of quinonyl and other oxygen-containing functionalities is also found to increase, often to a greater extent than the carboxyl groups. This journal is © The Royal Society of Chemistry.

Glassy carbon spherical powder (10-20 microm diameter) modified with cysteine methyl ester is found to be an inexpensive, novel material for the rapid removal of large quantities of toxic heavy metal ions such as Cd(II), Cu(II) and As(III) from aqueous media, with wide ranging potential applications such as third world drinking water filtration or environmental cleanup.

A convenient one-pot preparation of 9-fluorenylmethoxycarbonyl-L-p-azidophenylalanine is described.

The crystal structure reported for the title compound, C 12 H 14 ClNO 4 S, (I), is the first for a sulfamoyl chloride

A self-consistent terminology for partitioning data is presented. Ratios of the concentration of a component in two phases are termed partition coefficients and given the symbol D. Ratios of partition coefficients are termed exchange coefficients and given the symbol KD. The prefix “bulk” implies that these coefficients are weighted according to the proportions of coexisting phases. Bulk partition and bulk exchange coefficients are denoted by D and KD, respectively.

Two comments on a work by Murthy (1991) concerning the abundances of siderophile elements in the earth's mantle are presented. In the first comment it is asserted that the basis of Murthy's extrapolation is the assumption that the Gibbs free energy change for the partitioning reaction is independent of temperature, and as this is generally not a valid assumption thermodynamically, and as this is contradicted by most experimental data, the issue of mantle siderophile elements remains unresolved. In the second comment it is asserted that the extrapolation method used by Murthy does not appear to be valid thermodynamically, and that an extrapolation based on generally accepted thermodynamic assumptions yields different results. In a reply, Murthy takes issue with the comments.

The synthesis of [N-benzyl-N′-(Nα-benzyloxycarbonyl-L-asparaginyl)hydrazino]sulfonyl-L-prolyl-L-isoleucyl-L-valine methyl ester 4, a potential HIV-1 proteinase inhibitor, is described.

William Blake's comments about the sources of his creativity appear frequently in his prose and poetry and are fairly well known and often cited. His comments usually include references to other figures with whom he has conversed, and these conversations, Blake claims, provide him with inspiration for his poems. In his letters, he often writes of the visionary company he keeps and of how these conversations have influenced his work. On 6 May 1800, for example, Blake writes to William Hayley, "Thirteen years ago. I lost a brother & with his spirit I converse daily & hourly in the Spirit. & See him in my remembrance in the regions of my Imagination. I hear his advice & even now write from his Dictate.... I am the companion of Angels" (E 705).1 Blake's poetry also contains descriptions of conversations between the poems' speakers and other figures. In one example, the speaker of Jerusalem explains that every morning he awakens at sunrise and sees "the Saviour over me / Spreading his beams of love, & dictating the words of this mild song" (J 4.4-5). Of Blake's comments about his muses, Robert N. Essick writes

The title compounds, a novel class of peptide analogues in which an α-amino acid residue is replaced by a hydrazine-1, 2-diyl sulfonyl group -NHNRSO2-, are of potential interest as proteinase inhibitors. Synthetic approaches to such compounds and the X-ray molecular structures of two examples (16 and 28) are reported.

The partitioning of Pu and Sm between diopside/liquid and whitlockite/liquid has been investigated experimentally to evaluate the geochemical coherence of Pu and the light REEs. ^(Pu)D/^(Sm)D is 2 ~ for both diopsidic pyroxene and whitlockite. This small amount of fractionation would be decreased further if Pu were compared to Ce or Nd. Our experimental results thus validate the suggestion that Pu behaves as a LREE during igneous processes in reducing environments. Our data and the data of Ray et al. (1983) indicate that temperature rather than melt composition is the most important control on elemental partitioning. This is true even though we demonstrate that additions of only 1–2 wt.% of P2_O_5 to the diopside-anorthite-albite system change ^(Pu)D_(cpx) by a factor of two. Our data suggest that P_2O_5 in aluminosilicate melts serves as a complexing agent for the actinides and lanthanides.

Although the moon is depleted in volatile elements compared to the earth, these depletions are not in accord with simple volatility. For example, the Cs/Rb ratios of the earth and moon inferred from basalt are approximately one seventh and one half of the CI ratio, respectively. Volatility considerations alone predict that the lunar Cs/Rb ratio should be equal to or lower than the terrestrial ratio if the moon was derived entirely from earth mantle material. Thus hypotheses such as rotational fission which invoke derivation of lunar material entirely from the earth's mantle may be excluded. The collisional ejection hypothesis of lunar origin requires at least 18 percent of lunar material to be derived from a projectile with dehydrated CI composition to match the lunar Cs/Rb ratio, and 25-50 percent to match both the lunar Cs/Rb ratio and absolute concentrations of Cs and Rb. It remains to be demonstrated that this relatively large contribution of projectile material is consistent with other elemental abundances and element ratios in the moon.

The minor-element/major-element trends among the ureilites were investigated using electron microprobe data on olivine and pigeonite cores in eight low-shock ureilites. The results show well-defined correlations between Fe/X (where X is one of the minor elements Mn, Cr, Ca, Al, Ti, P, or Ni) and Fe/Mg ratios. For the lithophile minor elements, these trends are linear, with positive slope, and pass through or near the origin, indicating various degrees of FeO reduction of the parent magmas. The trends shown by P and Ni are consistent with this interpretation and require, in addition, equilibrium crystallization of 20-27 mole pct metal. A model is proposed for generation and crystallization of ureilite parent magmas, which predicts that the ureilite parent body had a differentiated crust, did not have a core, and was at least 235 km in radius.

Molar olivine/liquid partition coefficients for Mg, Fe, Mn and Ni are shown to be linearly correlated. These correlations appear to be independent of temperature, pressure and, to some extent, bulk composition and are best explained by the dominance of change-of-state thermodynamics during partitioning. The correlations presented here, when coupled with considerations of olivine stoichiometry, allow (olivine/basalt) partition coeficients of Mg, Fe, Mn and Ni to be predicted if the composition of the basalt is known. Since the correlations hold for major, minor and trace elements and for both “compatible” and “incompatible” elements, the inferences drawn from this study appear to have general relevance.

Previous estimates of the composition of the EPB have tacitly assumed chondritic abundances of refractory LIL elements. A model is presented here which utilizes refractory element ratios instead. Consideration of these ratios and of known olivine-liquid partition coefficients for Sc, Mg and Si imply that the EPB mantle may be accurately modeled as a simple mixture of 25 percent eucrite + 75 percent olivine. The model also implies that eucrites such as Juvinas and Sioux County were derived by large degrees of partial melting (20-30 percent). Comparison of the model EPB mantle to known meteorite classes indicates a similarity between the element abundances of the EPB and C3 chondrites.

N(α)-Benzyloxycarbonyl-N(τ)-phenacyl-L-histidine (5) and N(α)-benzyloxycarbonyl-N(π)-phenacyl-L-histidine (6) have been prepared. Under carboxy-activating conditions which cause gross racemisation of (5), (6) yields optically pure peptide. N(α)-t-Butoxycarbonyl-N(π)-phenacyl-L-histidine (7) has also been prepared and the practicability of the N(π)-phenacyl protective group (which is unchanged by strong aqueous or anhydrous acids and essentially unchanged by aqueous alkali, but which is quantitatively cleaved on treatment with zinc–acetic acid or on photolysis) has been demonstrated in a synthesis of thyroliberin.

New experimental data on the partitioning of siderophile and chalcophile elements among metallic and silicate phases may be used to constrain hypotheses of core formation in the Earth. Three current hypotheses can explain gross features of mantle geochemistry, but none predicts siderophile and chalcophile element abundances to within a factor of two of observed values. Either our understanding of metal-silicate interactions and/or our understanding of the early Earth requires revision.

Theoretical lunar mantle seismic velocity and density profiles were calculated for a series of specific bulk composition models, thermal models, and evolutionary models. It was found that most of the calculated seismic profiles are in qualitative agreement with the Nakamura (1983) observational mantle seismic velocity model. With respect to the density modeling results, the most interesting finding is that none of the considered models yield mantle density increases that are sufficient to match the adapted upper bound on the lunar moment-of-inertia factor (0.3928). The results suggest that the moon possesses a dense metallic core with a mass in the range of 1 to 4 percent of the lunar mass and that the alumina-rich models of Morgan et al. (1978) and Taylor (1982) are best able to match the middle mantle velocity increase that characterizes the Nakamura model.

Two simple methods of differentiating π- and τ-derivatised histidines unambiguously are described. The first involves conversion into one of the two known im-methyl-L-histidines, which, to avoid all possible confusion arising from ambiguous nomenclature and previous work, have been correlated with N(α)-t-butoxycarbonyl-N(π)-benzyloxymethyl-L-histidine, whose structure has been established by X-ray crystallography. The second method, which is appropriate for im-substituents of type RCH2–, involves the measurement of nuclear Overhauser effects. If the substituent is at the π-position, the CH2 signal is enhanced if the low-field adjacent proton between the heterocyclic nitrogens is irradiated, but not if the high-field, more distant, ring proton is irradiated. If the substituent is at the τ-position, the CH, signal is enhanced whichever of the equidistant ring protons is irradiated.

The chronologies of the Shergotty, Zagami, ALHA 77005, and EETA 79001 meteorites were reexamined on the basis of shergottites' petrography and mineral chemistry data. Among the various isochrons, the concordant Rb-Sr (about 180 Myr) and U-Th-Pb (about 190 Myr) internal isochrons are interpreted as representing the time of igneous crystallization, while the Rb-Sr, Sm-Nd, and Pb-Pb whole-rock isochrons are interpreted as mixing lines, and are reasonably attributed to igneous processes such as wall-rock assimilation and magma mixing. If the approximated age of less than 200 Myr is correct, the shergottites represent the youngest known extraterrestrial basalts. This conclusion supports the hypothesis that the SNC meteorites are samples of Mars.

Fission and alpha track radiography techniques have been used to measure partition coefficients (D) at trace (ppm) concentration levels for the actinide elements Th, U, and Pu between synthetic whitlockite and coexisting “haplobasaltic” silicate liquid at 1 bar pressure and 1250°C at oxygen fugacities from 10^(−8.5) and 10^(−0.7) bars. Pu is much more readily incorporated into crystalline phases than is U or Th under reducing conditions (fO_2 = 10^(−8.5)), because Pu is primarily trivalent, whereas U and Th are tetravalent. Definitive valence state assignments cannot be made, but our best estimates of corrected partition coefficients for Pu^(+3), Pu^(+4), Th^(+4), U^(+4), and U^(+6) are, for whitlockite 3.6/

Determination des constantes d'equilibre des reactions RhL 2 (CO)Y+PPN + Z − ⇄RhL 2 (CO)Z+PPN + Y − ou PPN=bis-triphenylphosphoranylidene d'ammonium. Etude realisee avec une serie d'anions respectivement pour L=Ph 3 P et L=Ph 3 As au moyen de la spectrometrie IR. Cette etude montre un large domaine d'affinite anionique pour les complexes du rhodium

The partitioning of Ir, Ge, Ga, W, Cr, Au, P, and Ni between solid metal and metallic liquid is investigated as a function of temperature and the S-concentration of the metallic liquid. The partition coefficients for siderophile elements, such as Ir, W, Ga, and Ge, are found to increase by factors of 10-100 as the S-concentration of the metallic liquid increases from 0-30 wt percent. Partition coefficients for other siderophile elements, such as Ni, Au, and P, increase by factors of only 2-3. In contrast, a decrease is seen in the partition coefficients for the more chalcophile element Cr. These experimentally determined coefficients are used in conjunction with a fractional crystallization model to reproduce the geochemical behavior of Ni, P, Au, and Ir during the magmatic evolution of groups IIAB, IIIAB, IVA and IVB iron meteorites. The mean S-concentration for each group increases in the order IVB, IVA, IIIAB, IIAB, which is in accordance with cosmochemical prediction. However, the geochemical behavior of Ge, Ga, W, and Cr cannot be reproduced in an internally consistent way. It is concluded that the magmatic histories of these iron meteorite groups are more complex than has been generally assumed.

Measurements of solid metal/liquid metal trace element partition coefficients, which are used to interpret the crystallization history of magmatic iron meteorite groups differ greatly between different research groups, using different experimental techniques. Specifically, partition coefficients measured utilizing 'static' experiments which approach equilibrium cannot be reconciled with the results of 'dynamic' experiments which mimic fractional crystallization. We report new tests of our 'static' experimental technique and demonstrate that our methodology yields reliable equilibrium values for Ni, P and Ge partition coefficients. Partition coefficients in the Fe-Ni-S-P system are well matched by interpolation between the Fe-Ni-S and Fe-Ni-P subsystems. In contrast, the predictions of 'dynamic' experiments do not agree with our measurements and, consequently, the ability of 'dynamic' experiments to reproduce iron meteorite Ge vs. Ni fractionation trends successfully must be regarded as fortuitous.

Two very different sets of Pu-244/U-238 ratios have been reported for early solar system materials, one high and the other low, and this paper examines how one of these groups may yield an incorrect ratio. Recently measured partition coefficients for Pu and Sm (Jones, 1981) are used to evaluate Pu-Nd fractionation during achondrite genesis, and Pu-244/U-238 ratios of chondrites, achondrites, and Ca-Al-rich inclusions are compared and discussed. A low Pu-244/U-238 ratio is favored, and some implications of this low ratio for galactic nucleosynthesis and meteorite age dating are briefly discussed.

We have used an electron microprobe or scanning electron microscope to analyze the Ag produced by exposure of Ilford nuclear emulsions to ^(151)Sm beta particles. The low beam currents of the SEM yielded satisfactory results while the higher current density of the microprobe produced variable amounts of volatilization of the organic constituents of the emulsion. Nonlinearities in Ag counting rate vs. exposure time curves were found at both high and low Ag concentrations. Two different types (mechanisms?) of emulsion fading were observed, one operating on an hour, the other on a day, time scale. The low-Ag nonlinearities are perhaps explained by either dose-dependent short time scale fading or by the requirement of multiple hits to render some AgBr grains developable.

Abundances of elements in shergottite, nakhlite, and Chassigny meteorites which originated on a single planet, the shergottite parent body (SPB), were examined with the aim of elucidating the chemical conditions of metal separation and core formation in the SPB and of testing present models of planetary core formation. Using partition coefficients and the SPB mantle composition determined in earlier studies, the abundances of Ag, Au, Co, Ga, Mo, Ni, P, Re, S, and W were modeled, with free parameters being oxygen fugacity, proportion of solid metal formed, proportion of metallic liquid formed, and proportion of silicate that is molten. It is shown that the abundances of all elements (except Mo) could be reproduced using models with these four free parameters. In contrast to the SPB, an equivalent model used to predict element abundances in the earth's mantle was shown by Jones and Drake (1986) to be inadequate; there is at present no hypothesis capable of quantitatively reproducing the elemental abundances of the earth's mantle. The contrast suggests that these two terrestrial planets (assuming that the SPB is Mars) may have accreted or differentiated differently.

A three-component model for the moon's bulk composition was developed on the basis of the results of Delano (1986) on lunar pristine glasses. This suite of models is based on the following two assumptions: (1) that the early moon differentiated into two primary reservoirs, a FeO-rich magma ocean and an olivine-rich residuum of about Fo(90); and (2) that this magma ocean then differentiated into an olivine-dominated cumulate, about equal to or greater than Fo(80), and a primitive liquid composition. Because serious uncertainties remain concerning the moon's complex differentiation history, this three-component model does not yield a single unique composition for the bulk silicate moon; instead, it yields a range of restricted compositions that are permitted within the conceptual framework of the model.

A detailed study of the U distribution of the St. Severin chondrite has been made by fission track radiography in order to clarify the interpretation of fission Xe thermal release data in terms of the mineralogical location of the fission Xe within the meteorite. This is of importance because the ^(244)Pu/^(238)U ratio for St. Severin has been widely adopted as the average solar system value. The U contents of the constituent minerals cannot account for the total rock U which, instead, appears to be primarily localized on grain boundaries. The greatest localizations of U are in olivine-poor, orthopyroxene-rich ‘clasts’. Our data coupled with those of Podosek (1970a) show that ^(244)Pu in St. Severin was also located on grain boundaries and that the bulk of Pu and U are unfractionated within this meteorite. Due to recoil, the ^(244)Pu fission Xe is found in 10 micron surface layers on major phases. Assuming that the grain boundaries (on which the Pu was located) was formed during metamorphism, the ^(244)Pu/^(238)U ratio for St. Severin applies to a time subsequent to the textural recrystallization of the meteorite. Our data support the interpretation of Podosek and our best estimate of the solar system ^(244)Pu/^(238)U is 0.015.

X-Ray analysis of N(α)-t-butoxycarbonyl-N(π)-benzyloxymethyl-L-histidine hydrate has confirmed that the im-protecting group is located on the π-nitrogen atom, in agreement with deductions from n.m.r. coupling constants.

The activities and partial molar heats of mixing have been determined in the liquid Cu−Sn system at 1320°C and the liquid Cu−Au system at 1460°C. The experimental technique consisted of the analysis of Knudsen cell effusates with a T.O.F. mass spectrometer. The ion current ratio for the alloy components was measured for each system over a range of temperature and composition and the thermodynamic values calculated by a modified Gibbs-Duhem equation. Both systems exhibited negative deviations from ideal behavior. The results can be partially represented by the equations $$\begin{gathered} \log \gamma _{Cu} = - 0.0175x^2 _{Sn} - 0.302 (0 \leqslant x_{Cu} \leqslant 0.20) \hfill \\ log \gamma _{Sn} = - 0.342x^2 _{Cu} + 1.084(0 \leqslant x_{Sn} \leqslant 0.20) \hfill \\ \end{gathered} $$ for the Cu−Sn system at 1320°C and by $$\begin{gathered} \log \gamma _{Cu} = - 0.703x^2 _{Au} - 0.083(0 \leqslant x_{Cu} \leqslant 0.52) \hfill \\ \log \gamma _{Au} = - 1.057x^2 _{Cu} + 0.098(0 \leqslant x_{Au} \leqslant 0.47) \hfill \\ \end{gathered} $$ for the Cu−Au system at 1460°C.

The change of energy of an atom of hydrogen when submitted to an electric field has been calculated by Epstein. If W denotes the total energy of an atom, then the change in energy Δ W, due to the field F, is given by ΔW = - 3 h 2 F/8 π 2 m E ( n 2 - n 1 ) ( n 1 + n 2 + n 3 ) + 17 e 2 F 2 /(16 π R H ) 2 m Z ( n 1 , n 2 , n 3 ), where R H is Rydberg's constant for hydrogen and Z ( n 1 , n 2 , n 3 ) = ( n 1 + n 2 + n 3 ) 6 {1 - 3/17 ( n 1 - n 2 /( n 1 + n 2 + n 3 ) 2 - 9/17 ( n 3 / n 1 + n 2 + n 3 ) 2 }, and n 1 and n 2 are parabolic quantum numbers and n 3 is the equatorial quantum number.

The method of measuring the derivatives of the earth’s magnetic field which is proposed depends on the fact that a small steady magnetic field will modify the e.m.f. induced in the secondary coil of a detector with a core of magnetizable material possessing high initial permeability and a high rate of increase of the permeability with the strength of the magnetizing field. It is shown that a detector of this type is equivalent to an inductor coil rotating with angular speed equal to the periodicity of the alternating magnetizing field.

Comparison of the acetyl-, trifluoroacetyl-, benzyloxycarbonyl-, methoxycarbonyl-, ethoxycarbonyl, methylaminocarbonyl, phenylaminocarbonyl-, phthanoyl-, and stearoyl-derivatives of glycylleucylphenylalanine methyl ester has shown that acetyl derivative is the most volatile. The relative abundances of the sequence ions in the mass spectra od these compounds have been determined and compared: the acetyl derivative provides the best combination of volatility and abundance of sequence ions. Evidence is presented to show that the use of acid-catalysed esterification procedure for the chemical modification of peptides prior to mas spectrometric investigation can lead to degraded derivatives.

The activities and partial molar heats of mixing have been determined for the liquid Ge-Cu system at 1525°C and the liquid Ge-Au system at 1400°C. The experimental technique consisted of analyzing Knudsen cell effusates with a TOF mass spectrometer. The ion current ratios for the monomeric vapor species were measured as a function of temperature and composition and the thermodynamic properties calculated using a modified form of the Gibbs-Duhem equations. Both systems exhibited negative deviations from ideal behavior. The results for the Raoultian activity coefficients can be partially represented by $$\begin{gathered} \log \gamma _{Ge} = - 2.521X_{Cu}^2 + 0.948 (0 \leqslant X_{Ge} \leqslant 0.2) \hfill \\ \log \gamma _{Cu} = - 0.048X_{Ge}^2 - 0.466 (0 \leqslant X_{Cu} \leqslant 0.2) \hfill \\ \end{gathered} $$ for the Ge-Cu system at 1525°C and by $$\begin{gathered} \log \gamma _{Ge} = - 2.327X_{Au}^2 + 0.465 (0 \leqslant X_{Ge} \leqslant 0.35) \hfill \\ \log \gamma _{Au} = - 0.510X_{Ge}^2 - 0.489 (0 \leqslant X_{Au} \leqslant 0.30) \hfill \\ \end{gathered} $$ for the Ge-Au system at 1400°C. An experimental technique is presented for determining the contribution of dissociative ionization of polymer species to the measured monomeric ion current ratio . The effect of dissociative ionization of the germanium polymer species present in the Knudsen ceil effusate was determined to be negligible.