Mixtures of monomeric and dimeric surfactants: hydrophobic chain length and spacer group length effects on non ideality

Critical micelle concentrations of the Cm TAB+12- s-12 (s=3, 4, 5 and m=10, 12, 14, 16) binary systems have been determined, through conductivity and fluorescence measurements, at 298 K. Application of different theoretical approaches to explain mixed micellization shows that non-ideality of the binary systems follows the trend C16TAB+12-3-12相似文献   

Raman spectroscopic study of the conformational change of 12-crown-4 due to cation capture

Raman spectra of the Li⁺, Na⁺, K⁺, NH⁺₄, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Pb²⁺ complexes of 12-crown-4 and also 12-crown-4 in various states are observed. The spectra of 12-crown-4 change remarkably by complex formation with cations. Normal vibration calculations of various conformations of 12-crown-4 are carried out. On the basis of the observed spectra and the results of the calculations, the conformation of 12-crown-4 in the Li⁺, Na⁺, K⁺, NH⁺₄, Mg²⁺ complexes is found to have approximate D_2d symmetry, while that in the Ca²⁺, Sr²⁺, Ba²⁺ complexes is found to have approximate C_2V symmetry.     

Preparation and Photocatalytic Activity of Ce,H3PW12O40 co-doped TiO2 Hollow Fibers

A series of Ce, H3PW12O40 co-doped TiO2 hollow fibers photocatalysts have been prepared by sol-gel method using ammonium ceric nitrate, H3PW12O40 and tetrabutyltitanate as precursors and cotton fibers as template, followed by calcination at 500 ℃ in N2 atmosphere for 2 h. Scanning electron microscopy, X-ray diffraction, nitrogen adsorption-desorption mea- surements, and UV-Vis spectroscopy are employed to characterize the morphology, crystal structure, surface structure, and optical absorption properties of the samples. The photo- catalytic performance of the samples has been studied by photodegradation phenol in water under UV and visible light irradiation. The results show that the TiO2 fiber materials have hollow structures, and the co-doped TiO2 hollow fibers exhibit higher photocatalytic activities for the degradation of phenol than un-doped, single-doped TiO2 hollow fibers under UV and visible light. In addition, the recyclability of co-doped TiO2 fibers is also confirmed that the TiO2 fiber retains ca. 90% of its activity after being used four times. It is shown that the co-doped TiO2 fibers can be activated by visible light and may be potentially applied to the treatment of water contaminated by organic pollutants. The synergistic effect of Ce and H3PW12O40 co-doping plays an important role in improving the photocatalytic activity.     

已烯自由基阳离子的密度泛函理论研究

使用密度泛函理论B3LYP方法和6-31G(d,p),6-31+G(d,p),6-311G(d,p)及6- 311+G(d,p)基组,分别对1-C_6H_(12)~+,2-C_6H_(12)~+和3-C_6H_(12)~+的各种构 象进行了几何构型优化,并在B3LYP/6-311G(d,p)水平上进行了频率分析计算,在 各优化构型上,使用B3LYP和MP2(full)方法进行了超精细结构的计算。计算的3- C_6H_(12)~+的超精细偶合常数比以往的计算结果更好;1-C_6H_(12)~+和2-C_6H_ (12)~+的超精细偶合常数目前尚无实验数据报道,本计算预言了它们的超精细偶合 常数和最稳定构型。     

M+(12-crown-4) supramolecular cations (M+ = Na+, K+, Rb+, and NH4+) within Ni(2-thioxo-1,3-dithiole-4,5-dithiolate)2 molecular conductor

Monovalent cations (M+ = Na+, K+, Rb+, and NH4+) and 12-crown-4 were assembled to new supramolecular cation (SC+) structures of the M+(12-crown-4)n (n = 1 and 2), which were incorporated into the electrically conducting Ni(dmit)2 salts (dmit = 2-thioxo-1,3-dithiole-4,5-dithiolate). The Na+, K+, and Rb+ salts are isostructural with a stoichiometry of the M+(12-crown-4)2[Ni(dmit)2]4, while the NH4+ salt has a stoichiometry of NH4+(12-crown-4)[Ni(dmit)2]3(CH3CN)2. The electrical conductivities of the Na+, K+, Rb+, and NH4+ salts at room temperature are 7.87, 4.46, 0.78, and 0.14 S cm-1, respectively, with a semiconducting temperature dependence. The SC+ structures of the Na+, K+, and Rb+ salts have an ion-capturing sandwich-type cavity of M+(12-crown-4)2, in which the M+ ion is coordinated by eight oxygen atoms of the two 12-crown-4 molecules. On the other hand, the NH4+ ion is coordinated by four oxygen atoms of the 12-crown-4 molecule. Judging from the M(+)-O distances, thermal parameters of oxygen atoms, and vibration spectra, the thermal fluctuation of the Na+(12-crown-4)2 structure is larger than those of K+(12-crown-4)2 and Rb+(12-crown-4)2. The SC+ unit with the larger alkali metal cation gave a stress to the Ni(dmit)2 column, and the SC+ structure changed the pi-pi overlap mode and electrically conducting behavior.     

Mass spectrometric analysis of the interactions between CP12, a chloroplast protein, and metal ions: a possible regulatory role within a PRK/GAPDH/CP12 complex

The small chloroplast protein CP12 plays the role of a protein linker in the assembly process of a PRK/GAPDH/CP12 complex that is involved in CO2 assimilation in photosynthetic organisms. The redox state of CP12 regulates its role as a protein linker. Only the oxidized protein, with two disulfide bonds, is active in complex formation. Several observations indicating that CP12 might bind a metal ion led us to screen the binding of different metal ions on oxidized or reduced CP12 using non-covalent electrospray ionization mass spectrometry (ESI-MS) experiments. The oxidized protein bound specifically Cu2+ and Ni2+ (Kd of 26+/-1 microM and 11+/-1 microM, respectively); other cations such as Fe2+ and Zn2+ did not bind, while cations such as Cd2+ formed non-specific adducts to CP12. Similar results were obtained for metal ions on screening with the reduced CP12. Interestingly, the present results suggest that Cu2+ catalyzes the re-formation of the disulfide bonds of the reduced CP12, leading to recovery of the fully oxidized CP12 that is then able to bind a Cu2+ ion. Finally the high similarity between CP12 and copper chaperones from Arabidopsis thaliana, as judged by hydrophobic cluster analysis, provides additional evidence for the relevance of metal binding for the in vivo situation. The findings that CP12 is able to bind a metal ion, and that Cu2+ catalyzes the oxidation of the thiol groups of CP12, are new characteristics of this protein that may prove to be important in the regulation of the assembly process of the PRK/GAPDH/CP12 complex.     

Photoinduced electron transfer in a triad that can be assembled/disassembled by two different external inputs. Toward molecular-level electrical extension cables

We have designed, synthesized, and investigated a self-assembling supramolecular system which mimics, at a molecular level, the function performed by a macroscopic electrical extension cable. The system is made up of three components, 12+, 2-H3+, and 3. Component 12+ consists of two moieties: a [Ru(bpy)3]2+ unit, which plays the role of an electron donor under light excitation, and a DB24C8 crown ether, which fulfills the function of a socket. The wire-type component 2-H3+ is also composed of two moieties, a secondary dialkylammonium-ion center and a bipyridinium unit, which thread into the DB24C8 crown-ether socket of 12+ and the 1/5DN38C10 crown-ether socket 3, respectively. The photochemical, photophysical, and electrochemical properties of the three separated components, of the 12+ superset 2-H3+ and 2-H3+ subset 3 dyads, and of the 12+ superset 2-H3+ subset 3 triad have been investigated in CH2Cl2 solution containing 2% MeCN. Reversible connection/disconnection of the two plug/socket systems can be controlled independently by acid/base and redox stimulation. The behavior of the various different dyads and triad has been monitored by light absorption and emission spectroscopies, as well as by electrochemical techniques. In the fully connected 12+ superset 2-H3+ subset 3 triad, light excitation of the [Ru(bpy)3]2+ unit of component 12+ is followed by electron transfer (k = 2.8 x 108 s-1) to the bipyridinium unit of component 2-H3+, which is plugged into component 3. Possible schemes to obtain improved molecular-level electrical extension cables are discussed.     

Synthesis, properties, and oxidizing ability of areno-annulated 1,3-dimethyl-10-phenylcyclohepta[4,5]pyrrolo[2,3-d]pyrimidine- 2,4(1,3H)-dionylium ions

[structures: see text] Novel areno-annulated 1,3-dimethyl-10-phenylcyclohepta[4,5]pyrrolo[2,3-d]pyrimidine-2,4(1,3H)-dionylium ions 12a,b+ x BF4(-) and 16a+ x BF4(-) were synthesized by three-step reactions, starting from the reactions of benzo[b]tropone and naphtho[2,3-d]tropone with 6-anilino-1,3-dimethyluracil. Structural characteristics of 12a,b+ and 16a+ were clarified on inspection of the UV-vis and NMR spectral data as well as by X-ray crystal analyses. The stability of cations 12a,b+ and 16a+ is expressed by the pK(R+) values which were determined spectrophotometrically as the values of ca. 0.5-9.0. The pK(R+) value of the naphtho[b]tropylium ion 4+ was clarified to be much lower, at <0. The electrochemical reduction of 12a,b+ and 16a+ exhibited reduction potentials at -0.46 to -0.67 (V vs Ag/AgNO3) upon cyclic voltammetry (CV). The reduction potentials of the benzotropylium ion and cation 4+ were -0.26 and -0.09 V, respectively. In a search for reactivity, reactions of 12a,b+ x BF4(-) with some nucleophiles, hydride and diethylamine, were carried out. Although the reactions of 12a+ x BF4(-) afforded C11 adduct 19 as a single product, the addition reactions of 12b+ x BF4(-) proceeded at both C9 and C11. The attempted reduction of methyl benzoylformate by using 21 was carried out unsuccessfully. The photoinduced oxidation reaction of 12a,b+ x BF4(-) and 16a+ x BF4(-) toward some amines under aerobic conditions was carried out to give the corresponding imines (isolated by converting to the corresponding 2,4-dinitrophenylhydrazones) with the recycling number of 3.6-21.7.     

CaAl12O19基质中Eu2+-Cr3+的能量传递与发光性质

在还原气氛下高温固相法合成了CaAl12O19:Eu2+,Cr3+荧光粉.样品光谱显示:Eu2+发射带与Cr3+吸收带有重叠,具备Eu2+-Cr3+之间发生能量传递必要条件.在290 nm近紫外光激发下,单掺杂Eu2+和Cr3+时样品均无691 nm发射,仅在Eu2+,Cr3+共掺时才出现691 nm发射,这证明Eu2+和Cr3+之间发生了能量传递,且监测691 nm时样品的激发光谱也证实了这一点.CaAl12O19:1%Eu2+,x%Cr3+样品组的发射光谱研究表明:增大x能提高Cr3+红光与Eu2+蓝紫光发射强度之比及Eu2+-Cr3+之间能量传递效率.CaAl12O19:2%Cr3+,x%Eu2+样品组的激发光谱分析表明:x>2时,Cr3+在415 nm处的吸收效率相对于565 nm有显著提高.还对样品CaAl12O19:1%Eu2+,1%Cr3+荧光寿命和能量传递速率进行了简单分析.     

Li+ transport in lithium sulfonylimide-oligo(ethylene oxide) ionic liquids and oligo(ethylene oxide) doped with LiTFSI

The Li+ environment and transport in an ionic liquid (IL) comprised of Li+ and an anion of bis(trifluoromethanesulfonyl)imide anion (TFSI-) tethered to oligoethylene oxide (EO) (EO(12)TFSI-/Li+) were determined and compared to those in a binary solution of the oligoethylene oxide with LiTFSI salt (EO(12)/LiTFSI) by using molecular dynamics (MD) simulations and AC conductivity measurements. The latter revealed that the AC conductivity is 1 to 2 orders of magnitude less in the IL compared to the oligoether/salt binary electrolyte with greater differences being observed at lower temperatures. The conductivity of these electrolytes was accurately predicted by MD simulations, which were used in conjunction with a microscopic model to determine mechanisms of Li+ transport. It was discerned that structure-diffusion of the Li+ cation in the binary electrolyte (EO(12)/LiTFSI-) was similar to that in EO(12)TFSI-/Li+ IL at high temperature (>363 K), thus, one can estimate conductivity of IL at this temperature range if one knows the structure-diffusion of Li+ in the binary electrolyte. However, the rate of structure-diffusion of Li+ in IL was found to slow more dramatically with decreasing temperature than in the binary electrolyte. Lithium motion together with EO(12) solvent accounted for 90% of Li+ transport in EO(12)/LiTFSI-, while the Li+ motion together with the EO(12)TFSI- anion contributed approximately half to the total Li+ transport but did not contribute to the charge transport in IL.     

Mechanistic analysis of the electrocatalytic properties of dissolved alpha and beta isomers of [SiW12O40]4- and solid [Ru(bipy)3]2[alpha-SiW12O40] on the reduction of nitrite in acidic aqueous media

Voltammetric studies on the reduction of alpha and beta isomers of the Keggin polyoxometalate anion [SiW12O40]4- reveal a series of electrochemically reversible processes in acidic aqueous media. In the presence of NO2-, catalytic current is detected in the potential region of the [SiW12O40]4-/5- process. Electronic spectroscopy and simulation of voltammetric data undertaken at variable [NO2-] and [H+] allow the following mechanism to be postulated, [SiW12O40]4- + e- <-->[SiW12O40]5-, H+ + HNO2 <--> NO+ + H2O, NO+ + [SiW12O40]5- --> NO + [SiW12O40]4-. The second-order rate constant for the rate-determining step is faster for the alpha isomer than for the beta one. This may be attributed to the different reversible potentials of -0.144 V (alpha isomer) and -0.036 V vs Ag/AgCl (beta isomer) and, hence, smaller driving force for an assumed outer sphere electron-transfer reaction in the case of beta isomer. A stable, water-insoluble, thin-film [Ru(bipy)3]2[alpha-SiW12O40] chemically modified electrode was generated electrochemically via ion-exchange of [Ru(bipy)3]2+ with Bu4N+ in the [Bu4N]4[alpha-SiW12O40] solid. The first reduction process with this modified electrode gives rise to the reaction [Ru(bipy)3]2[alpha-SiW12O40](solid) + H+(soln) + e- <--> H[Ru(bipy)3]2[alpha-SiW12O40](solid). The need to transfer a proton from the solution to the solid phase for charge neutralization purposes introduces a hydrogen-ion concentration dependence into this reaction, which is not found in the solution-phase study. Nevertheless, the voltammetric catalytic activity with respect to nitrite reduction is retained with the chemically modified electrode. However, nitrite catalysis with the [Ru(bipy)3]2[alpha-SiW12O40]-modified electrode is now independent of concentration of H+, rather than exhibiting a first-order dependence, and full mechanistic details for this process are unknown.     

Radial dose distribution around a heavy ion''s path

Ionization currents produced in a small wall-less ionization chamber located at varying distance from the 200 MeV Ni¹²⁺ ion's path traversing Ar gas were measured and utilized to construct a track structure model. Using the LET value of 200 MeV Ni¹²⁺ and G(Fe³⁺) in Fricke solutions (= 15.4) for fast electrons, we estimate G(Fe³⁺) for 200 MeV Ni¹²⁺ to be 5.0.     

Inhibitory effect of H_(3 + x)PMo_(12－x)V_xO_(40)-Ton the self-polymerization of methyl methacrylate

In this work,a series of molybdovanadophosphoric heteropoly acid quaternary ammonium salts H_(3+x)PMo_(12 -x)V_xO40-T were synthesized and employed as a reaction inhibitor in the selfpolymerization of methyl methacrylate(MMA).The polymerization inhibition effect of H_(3+x)PMoPMo_(12 -x)V_xO40-T)with different number of vanadium atoms and reaction dosages was investigated using differential scanning calorimetry(DSC).It shows that the inhibitory effect was improved with the increasing dosages of H_(3+x)PMoPMo_(12 -x)V_xO40-T),and the polymerization inhibition was also affected by the number of vanadium atoms in the H_(3+x)PMo_(12 -x)V_xO40-T .Furthermore,cyclic voltammograms(CV)was used to probe the mechanism of the inhibition reaction with H3+xPMo12xVxO40-T.The result of CV indicates that the inhibition reaction is an oxidation–reduction reaction.H_(3+x)PMo_(12 -x)V_xO40-T can react directly with the MMA monomer radicals,which eliminated the MMA monomers,and therefore the self-polymerization of the MMA can be effectively inhibited by H_(3+x)PMo_(12 -x)V_xO40-T.     

Reactions of transition-metal carbonyls with anhydrous HF

The reactions of a wide range of transition-metal carbonyls with anhydrous HF are described. In particular, Ru₃(CO)₁₂, Os₃(CO)₁₂ and Ir₄(CO)₁₂ give the solution stable [Ru₃(CO)₁₂H]⁺, [Ru(CO)₅H]⁺, [Os₃(CO)₁₂H]⁺, [Os(CO)₅H]⁺ and [Ir₄(CO)₁₂H₂]²⁺ respectively, which have been characterised by a combination of ¹H and ¹³C NMR spectroscopy.     

Electroactive hemoglobin-surfactant-polymer biomembrane-like films

Polyions complex 2C12N+ PSS- was prepared by reacting poly(sodium styrenesulfonate) (Na+ PSS-) with didodecyldimethylammonium bromide (2Cl2N+ Br-). Stable thin films made from 2C12N+ PSS- with incorporated redox protein hemoglobin (Hb) on pyrolytic graphite (PG) electrodes were then characterized by electrochemistry and other techniques. Cyclic voltammetry (CV) of Hb-2C12N+ PSS- films showed a pair of well-defined and nearly reversible peaks for HbFe(III)/Fe(II) couple at about -0.17 V vs. saturated calomel electrode (SCE) in pH 5.5 buffers. The electron transfer rate between Hb and PG electrode was greatly facilitated in microenvironment of 2C12N+ PSS- films. Positions of Soret absorption band suggest that Hb keeps its secondary structure similar to its native state in 2C12N+ PSS- films at the medium pH. The results of X-ray diffraction and differential scanning calorimetry (DSC) suggest synthesized lipid 2C12N+ PSS- films have an ordered bilayer structure intercalated between PSS- polyion layers, and the incorporated Hb expands the layer spacing of the films. HbFe(I), a highly reduced form of Hb, might also be produced in these films at about -1.09 V, and could be used to catalytically reduce organohalide pollutants.     

Spiropentane mimics of nucleosides: analogues of 2'-deoxyadenosine and 2'-deoxyguanosine. Synthesis of all stereoisomers, isomeric assignment, and biological activity

Synthesis of spirocyclic analogues of 2'-deoxyadenosine and 2'-deoxyguanosine (12a-15a and 12b-15b) is described. Rhodium-catalyzed reaction of ethyl diazoacetate with methylenecyclopropane 19, obtained from 2-bromo-2-bromomethylcyclopropane 17 via debromination (16), reduction (18), and acetylation (19), gave a mixture of all four isomeric spiropentanes 20a-20d. Hydrolysis afforded hydroxy carboxylic acids 21a-21d. Acetylation of separated proximal + medial-syn isomers 21a + 21b and medial anti + distal isomers 21c + 21d furnished acetates 22a + 22b and 22c + 22d. Curtius rearrangement effected by diphenylphosphoryl azide in tert-butyl alcohol performed separately with mixtures 22a + 22b and 22c + 22d led to BOC-amino spiropentanes 23a + 23b and 23c + 23d. After deacetylation all isomers 24a-24d were separated and deprotected to give aminospiropentane hydrochlorides 25a-25d. Free bases were of limited stability. The heterocyclic moieties were introduced into individual isomers 25a-25d via 6-chloropurine derivatives 26a-26d or 30a-30d. Ammonolysis of 26a-26d furnished the adenine isomeric series 12a-15a, whereas guanine derivatives 12b-15b were obtained by hydrolysis of 30a-30d with formic acid. The isomeric assignments followed from IR spectra of BOC-aminospiropentanes 24a-24d and NMR spectra of 12a-15a including NOE and (H,H) COSY. The proximal and medial-syn isomers 12a and 12b were modest inhibitors of human cytomegalovirus (HCMV) and Epstein-Barr virus (EBV) in culture, whereas the medial-anti isomer 12c was a substrate for adenosine deaminase. The distal isomer 15b was an anti-EBV agent. The medial-syn phosphoralaninate 34 was an effective inhibitor of HCMV replication in vitro. It was also active against herpes simplex virus type 1 (HSV-1), varicella zoster virus (VZV), human immunodeficiency virus (HIV-1), hepatitis B virus (HBV), and EBV with a varying degree of cytotoxicity.     

Special stability of cationic MPb12+ clusters and superalkali character of neutral MPb12 clusters (M = B, Al, Ga, In, and Tl)

The electronic structures and stabilities of cationic MPb12+ clusters (M = B, Al, Ga, In, and Tl) with 50 valence electrons are investigated within density functional theory. It is shown that, at the B3LYP/cc-pVDZ(-PP) and BPW91/cc-pVDZ(-PP) levels of theory, the structures of MPb12+ with icosahedra (I(h)) symmetry are energetically favorable, and their high stabilities may arise from the closed-shell nature of the pi subsystems which are subject to the 2(N(pi + 1)2 rule with N(pi = 1). In addition, the possessing of large nucleus-independent chemical shifts of the five kinds of clusters reflects the common aromatic character of these clusters. From the comparison of our studies on the binding energies and the highest occupied molecular orbital and the lowest unoccupied molecular orbital energy gaps, the cluster AlPb12+ has higher stability than the others and this is consistent with the recent mass-spectrometric discovery of Al-doped Pb(n)+ clusters, in which AlPb12+ is highly abundant. The same methods are used to search for the structures of the neutral MPb12 clusters. The calculations reveal that the most stable geometries of the BPb12 and GaPb12 clusters have I(h) symmetry, the AlPb12 and InPb12 clusters have T(h) symmetry, and the TlPb12 cluster has C5v symmetry. Furthermore, the vertical ionization potentials of the neutral MPb12 clusters are smaller than that of some alkali atoms, indicating that the neutral MPb12 clusters possess superalkali character.     

Electrochemistry and electrocatalysis with myoglobin in biomembrane-like surfactant-polymer 2C12N+PA- composite films

Biomembrane-like polyionic complex, 2C₁₂N⁺PA⁻, was prepared by reacting sodium polyacrylate (Na⁺PA⁻) with didodecyldimethylammonium bromide (2C₁₂N⁺Br⁻). Stable thin films made from 2C₁₂N⁺PA⁻, with incorporated myoglobin (Mb), on pyrolytic graphite (PG) electrodes were then characterized by electrochemistry and other techniques. Cyclic voltammetry of Mb-2C₁₂N⁺PA⁻ films showed a pair of well-defined quasi reversible peaks for MbFe(III)/Fe(II) couple at about −0.19 V versus SCE in pH 5.5 buffers. The electron transfer rate between Mb and PG electrodes was greatly facilitated in the microenvironment of 2C₁₂N⁺PA⁻ films. Square wave voltammetry data were used to estimate the apparent heterogeneous electron transfer rate constants by nonlinear regression analysis using a model featuring dispersion of formal potentials. Positions of Soret absorption bands suggested that Mb keeps its secondary structure similar to its native state in 2C₁₂N⁺PA⁻ films at the medium pH. The results of differential scanning calorimetry and X-ray diffraction suggest that synthesized 2C₁₂N⁺PA⁻ lipid films have an ordered multibilayer structure and the incorporated Mb does not disturb this structure. Oxygen was catalytically reduced by Mb-2C₁₂N⁺PA⁻ films with a significant decrease in the electrode potential. MbFe(I), a highly reduced form of Mb, was also produced in Mb-2C₁₂N⁺PA⁻ films at about –1.09 V, and could be used to catalytically reduce organohalide pollutants such as perchloroethylene (PCE) and trichloroethylene (TCE). The catalytic reduction peak currents had linear relationships with concentrations of PCE and TCE in a range of 10–100 μM. The potential applications of the film electrode as a sensor for detecting organohalides are discussed.     

Magnetic and electronic properties of CaCu3Cr4O12 and CaCu3Cr2Sb2O12 by first-principles density functional calculation

The electronic and magnetic properties of CaCu3Cr4O12 and CaCu3Cr2Sb2O12 are investigated by the use of the full-potential linearized augumented plane wave (FPLAPW) method. The calculated results indicate that CaCu3Cr4O12 is a ferrimagnetic and half-metallic compound, in good agreement with previous theoretical studies. CaCu3Cr2Sb2O12 is a ferrimagnetic semiconductor with a small gap of 0.136 eV. In both compounds, because Cr4+ 3d (d2) and Cr3+ 3d (d3) orbitals are less than half filled, the coupling between Cr-Cu is antiferromagnetic, whereas that between Cu-Cu and Cr-Cr is ferromagnetic. The total net spin moment is 5.0 and 3.0 microB for CaCu3Cr4O12 and CaCu3Cr2Sb2O12, respectively. In CaCu3Cr4O12, the 3d electrons of Cr4+ are delocalized, which strengthens the Cr-Cr ferromagnetic coupling. For CaCu3Cr2Sb2O12, the doping of nonmagnetic ion Sb5+ reduces the Cr-Cr ferromagnetic coupling, and the half-filled Cr3+ t2g (t2g3) makes the chromium 3d electrons localized. In addition, the ordering arrangement of the octahedral chromium and antimony ions also prevents the delocalization of electrons. Hence, CaCu3Cr2Sb2O12 shows insulating behavior, in agreement with the experimental observation.     

Effect of reticuloendothelial blockade on tissue distribution of 99mTc-labeled synthetic liposomes in Ehrlich solid tumor-bearing mice

The effect of a reticuloendothelial blockade was examined on the tissue distribution of 99mTc-labeled synthetic liposomes prepared from N,N-didodecyl-N alpha-[6-(trimethylammonio)hexanoyl]-L-alaninamide bromide (N+C5Ala2C12) in Ehrlich solid tumor-bearing mice. While a pre-dose of unlabeled phosphatidyl choline liposomes (natural liposomes) hardly influenced the tissue distribution of N+C5Ala2C12 liposomes, the pretreatment of dextran sulfate depressed the uptake in liver accompanied by increasing that in tumor and other tissues except the stomach. However, the extent of liver depression of N+C5Ala2C12 liposomes by dextran sulfate was lower than that of natural liposomes and the pre-dose of unlabeled natural liposomes had a minor effect on the tissue distribution of N+C5Ala2C12 liposomes compared with that of natural liposomes. In the liver uptake of N+C5Ala2C12 liposomes, it was suggested that Kupffer cell phagocytosis was not the main mechanism.