A three-dimensional ferromagnet, [Ni(dipn)]3[Cr(CN)6]2.3H2O (dipn = dipropylene triamine), based on a cubic Cr8Ni12 unit

The combination of Ni2+, dipropylenetriamine (dipn), and [Cr(CN)6]3- affords the cyanide-bridged bimetallic assembly, [Ni(dipn)]3[Cr(CN)6]2.3H2O (1). This compound crystallizes in cubic space group Pa, with a = b = c = 20.9742(7) A and Z = 8. A three-dimensional network is constructed on the basis of a Cr8Ni12 cubane unit formed by an alternate array of [Cr(CN)6]3- and [Ni(dipn)]2+ units through Cr-CN-Ni-NC-Cr edges. Cryomagnetic studies reveal a ferromagnetic interaction between Cr(III) and Ni(II) ions and a long-range ferromagnetic ordering below 42 K with very small coercive field. To the best of our knowledge, this compound is the first "complete ferromagnet" providing three-dimensional ferromagnetic interaction through a three-dimensional bridging structure that is based on a cubic unit among general metal-oxide and molecule-based magnets. Magnetooptical studies demonstrate a strong correlation between magnetic and optical properties.     

Photodissociation of polycrystalline and amorphous water ice films at 157 and 193 nm

The photodissociation dynamics of amorphous solid water (ASW) films and polycrystalline ice (PCI) films at a substrate temperature of 100 K have been investigated by analyzing the time-of-flight (TOF) mass spectra of photofragment hydrogen atoms at 157 and 193 nm. For PCI films, the TOF spectrum recorded at 157 nm could be characterized by a combination of three different (fast, medium, and slow) Maxwell-Boltzmann energy distributions, while that measured at 193 nm can be fitted in terms of solely a fast component. For ASW films, the TOF spectra measured at 157 and 193 nm were both dominated by the slow component, indicating that the photofragment H atoms are accommodated to the substrate temperature by collisions. H atom formation at 193 nm is attributed to the photodissociation of water species on the ice surface, while at 157 nm it is ascribable to a mixture of surface and bulk photodissociations. Atmospheric implications in the high latitude mesopause region of the Earth are discussed.     

Nonexistence of some linear codes over the field of order four

We consider the problem of determining $n_4(5,d)$, the smallest possible length $n$ for which an ${[n,5,d]}_4$ code of minimum distance $d$ over the field of order 4 exists. We prove the nonexistence of ${[g_4(5,d)+1,5,d]}_4$ codes for $d=31,47,48,59,60,61,62$ and the nonexistence of a ${[g_4(5,d),5,d]}_4$ code for $d=138$ using the geometric method through projective geometries, where $g_q(k,d)={\sum }_{i=0}^{k?1}?d∕q^i?$. This yields to determine the exact values of $n_4(5,d)$ for these values of $d$. We also give the updated table for $n_4(5,d)$ for all $d$ except some known cases.     

Chiral recognition of apple procyanidins by complexation with oxotitanium phthalocyanine

A series of supramolecular complexes formed between oxotitanium(IV) phthalocyanine and apple procyanidins have exhibited characteristic bisignate CD signals in the Q region (ca. 700 nm). The helicity of the oligomeric procyanidins is proposed to be left-handed on the basis of the CD analyses. [structure: see text]     

Thermal physics in carbon nanotube growth kinetics

The growth of single wall carbon nanotubes (SWNTs) mediated by metal nanoparticles is considered within (i) the surface diffusion growth kinetics model coupled with (ii) a thermal model taking into account heat release of carbon adsorption-desorption on nanotube surface and carbon incorporation into the nanotube wall and (iii) carbon nanotube-inert gas collisional heat exchange. Numerical simulations performed together with analytical estimates reveal various temperature regimes occurring during SWNT growth. During the initial stage, which is characterized by SWNT lengths that are shorter than the surface diffusion length of carbon atoms adsorbed on the SWNT wall, the SWNT temperature remains constant and is significantly higher than that of the ambient gas. After this stage the SWNT temperature decreases towards that of gas and becomes nonuniformly distributed over the length of the SWNT. The rate of SWNT cooling depends on the SWNT-gas collisional energy transfer that, from molecular dynamics simulations, is seen to be efficient only in the SWNT radial direction. The decreasing SWNT temperature may lead to solidification of the catalytic metal nanoparticle terminating SWNT growth or triggering nucleation of a new carbon layer and growth of multiwall carbon nanotubes.     

Orientation of the alkyl side chains and glucopyranose rings in Langmuir–Blodgett films of a regioselectively substituted cellulose ether

An arrangement for the long alkyl side chains in a Langmuir–Blodgett (LB) film from regioselectively alkylated 2,3-di-O-octadecylcellulose on an Au-coated substrate was investigated using Fourier transform infrared reflection absorbance spectroscopy. The IR results indicated that the hydrophobic long alkyl side chains were forced to be repellent to the surface of water, resulting in deposition on the substrate, with it being tilted in the vertical direction, and further formed both hexagonal and orthorhombic crystalline structures up to 10 layers in the LB film. In addition, molecular modeling with CAChe software indicated that the optimized assembly of the side chains was supposed to own a vertical arrangement against the substrate surface after compression of the monolayer. This means that the conformation of 2₁ screw of the cellulose molecular chain may be altered by the compression to have an unusual conformation by a different φ–ψ dihedral angle such as onefold axis without a symmetry element.     

Parameters affecting the adhesion strength between a living cell and a colloid probe when measured by the atomic force microscope

In this study, we used the colloid probe atomic force microscopy (AFM) technique to investigate the adhesion force between a living cell and a silica colloid particle in a Leibovitz's L-15 medium (L-15). The L-15 liquid maintained the pharmaceutical conditions necessary to keep the cells alive in the outside environment during the AFM experiment. The force curves in such a system showed a steric repulsion in the compression force curve, due to the compression of the cells by the colloid probe, and an adhesion force in the decompression force curve, due to binding events between the cell and the probe. We also investigated for the first time how the position on the cell surface, the strength of the pushing force, and the residence time of the probe at the cell surface individually affected the adhesion force between a living cell and a 6.84 μm diameter silica colloid particle in L-15. The position of measuring the force on the cell surface was seen not to affect the value of the maximum adhesion force. The loading force was also seen not to notably affect the value of the maximum adhesion force, if it was small enough not to pierce and damage the cell. The residence time of the probe at the cell surface, however, clearly affected the adhesion force, where a longer residence time gave a larger maximum force. From these results, we could conclude that the AFM force measurements should be made using a loading force small enough not to damage the cell and a fixed residence time, when comparing results of different systems.     

Enantioselective alkylation of aldehydes catalyzed by a highly active titanium complex of 3-substituted unsymmetric BINOL

[reaction: see text] A titanium complex derived from 3-(3,5-diphenylphenyl)-BINOL exhibits an enhanced catalytic activity in the asymmetric alkylation of aldehydes, allowing the reduction of the catalyst amount to less than 1 mol % without deterioration in enantioselectivity.     

Dispersion and separation of small-diameter single-walled carbon nanotubes

The dispersion of small-diameter single-walled carbon nanotubes (SWNTs) produced by the CoMoCAT method in tetrahydrofuran (THF) with the use of amine was studied. The absorption, photoluminescence, and Raman spectroscopies showed that the dispersion and centrifugation process leads to an effective separation of metallic SWNTs from semiconducting SWNTs. Since this method is simple and convenient, it is highly applicable to an industrial utilization for widespread applications of SWNTs.     

1,3‐Dimethyl­isoguanine

The structure of 1,3‐dimethyl­isoguanine [or 6‐amino‐1,3‐dimethyl‐1H‐purin‐2(3H)‐one], C₇H₉N₅O, has been redetermined and the correct assignment of H atoms on the heterocycle is now reported. Inter­molecular hydrogen‐bonding inter­actions confirm that this form is the correct mol­ecular structure; this form is also in agreement with an earlier reported structure of the trihydrate form.