Side-chain liquid crystalline homo- and copolymethacrylates with a carbonate linkage between the benzylideneaniline mesogen and ethylene chain

Abstract

New liquid crystalline (LC) homo- and copolymethacrylates having a carbonate linkage between a benzylideneaniline mesogen and ethylene chain in the side chain were prepared by free radical polymerization of methacrylate derivatives comprising 4-cyano- and/or 4-methoxybenzylide-neaniline units using AIBN as an initiator. The structures of the polymers were characterized by FTIR, ¹HNMR, and elemental analyses. The LC properties were evaluated by differential scanning calorimetry (DSC), polarizing microscopic observation of textures and X-ray diffraction. These measurements showed that all the homo- and copolymers form nematic phases. The isotropization temperatures on composition exhibited a negative deviation from a linear relationship between them predicted by the Schroeder-Van Laar equation. This phenomenon might be caused mainly by an unusual geometry arising from a smaller bond angle in the carbonate linkage.     

Highly parity linked graphs

A graph G is k-linked if G has at least 2k vertices, and for any 2k vertices x ₁,x ₂, …, x _k ,y ₁,y ₂, …, y _k , G contains k pairwise disjoint paths P ₁, …, P _k such that P _i joins x _i and y _i for i = 1,2, …, k. We say that G is parity-k-linked if G is k-linked and, in addition, the paths P ₁, …, P _k can be chosen such that the parities of their length are prescribed. Thomassen [22] was the first to prove the existence of a function f(k) such that every f(k)-connected graph is parity-k-linked if the deletion of any 4k-3 vertices leaves a nonbipartite graph. In this paper, we will show that the above statement is still valid for 50k-connected graphs. This is the first result that connectivity which is a linear function of k guarantees the Erdős-Pósa type result for parity-k-linked graphs. Research partly supported by the Japan Society for the Promotion of Science for Young Scientists, by Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research and by Inoue Research Award for Young Scientists.     

Utilization of the pleiotropy of a peptidic aptamer to fabricate heterogeneous nanodot-containing multilayer nanostructures

Peptide aptamers (=binders) against inorganic materials often show a capacity for mineralization of their target atoms; thus they are able to function both as binding molecules and as mediators for mineralization. Although the mechanisms underlying these two properties of peptide aptamers are not yet fully understood, they have been used separately to fabricate various nanostructures. Here, we present a novel method of nanofabrication, in which binding and mineralization by a peptide aptamer are alternately utilized to assemble multilayered nanostructures comprised of metal loaded cage proteins ornamented with Ti-binding peptides.     

From an S(T) = 3 single-molecule magnet to diamagnetic ground state depending on the molecular packing of Mn(III)salen-type dimers decorated by N,N'-dicyano-1,4-naphthoquinonediiminate radicals

Two manganese(III) tetradentate Schiff-base dimers to which N,N'-dicyano-1,4-naphthoquinonediiminate (DCNNQI) radicals are attached have been selectively synthesized by varying the solvents used in the reactions: [Mn2(5-MeOsaltmen)2(DCNNQI)2].MeOH (1) and [Mn2(5-MeOsaltmen)(2)(DCNNQI)(2)] x 2CH2Cl2.2CH3CN (2) [5-MeOsaltmen2- = N,N'-(1,1,2,2-tetramethylethylene)bis(5-methoxysalicylideneiminate)]. These two complexes share the same molecular core, [(DCNNQI.-)-Mn(III)-(O)2-Mn(III)-(DCNNQI.-)], where -(O)2- is a biphenolate bridge in the out-of-plane dimerized [Mn(2)(5-MeOsaltmen)2]2+ moiety. However, their packing arrangements are completely different. Whereas complex 1 is found to be relatively isolated, strong intermolecular dimerization of the DCNNQI moieties (with the nearest contact being approximately 3.0 A) is observed in 2, forming a one-dimensional chain of [-Mn(III)-(O)2-Mn(III)-(DCNNQI.-)2-](infinity). The magnetic susceptibility of 1 can be modeled with an [S = 1/2, 2, 2, 1/2] four-spin system including strong antiferromagnetic Mn(III)/DCNNQI radical coupling (J(Mn/rad)/kB = -23 K) and ferromagnetic Mn(III)/Mn(III) coupling through the biphenolate bridge (J(Mn/Mn)/kB = +2.0 K). These interactions lead to an ST = 3 ground state that possesses significant uniaxial anisotropy (D(S=3)/kB = -2.1 K). Low-temperature ac and dc magnetic data of 1 reveal its single-molecule magnet behavior with quantum tunneling of the magnetization. By contrast, 2 possesses the diamagnetic ground state induced by dominating Mn(III)-Mn(III) antiferromagnetic interactions mediated by the diamagnetic DCNNQI dimers and/or pi-pi contact along the b axis.     

Characterization and activity analysis of catalytic water oxidation induced by hybridization of [(OH(2))(terpy)Mn(mu-O)(2)Mn(terpy)(OH(2))](3+) and clay compounds

Hybridization of [(OH(2))(terpy)Mn(mu-O)(2)Mn(terpy)(OH(2))](3+) (terpy= 2,2':6',2' '-terpyridine) (1) and mica clay yielded catalytic dioxygen (O(2)) evolution from water using a CeIV oxidant. The reaction was characterized by various spectroscopic measurements and a kinetic analysis of O(2) evolution. X-ray diffraction (XRD) data indicates the interlayer separation of mica changes upon intercalation of 1. The UV-vis diffuse reflectance (RD) and Mn K-edge X-ray absorption near-edge structure (XANES) data suggest that the oxidation state of the di-mu-oxo Mn(2) core is Mn(III)-Mn(IV), but it is not intact. In aqueous solution, the reaction of 1 with a large excess Ce(IV) oxidant led to decomposition of 1 to form MnO(4-) ion without O(2) evolution, most possibly by its disproportionation. However, MnO(4-) formation is suppressed by adsorption of 1 on clay. The maximum turnover number for O(2) evolution catalyzed by 1 adsorbed on mica and kaolin was 15 and 17, respectively, under the optimum conditions. The catalysis occurs in the interlayer space of mica or on the surface of kaolin, whereas MnO(4-) formation occurs in the liquid phase, involving local adsorption equilibria of adsorbed 1 at the interface between the clay surface and the liquid phase. The analysis of O(2) evolution activity showed that the catalysis requires cooperation of two equivalents of 1 adsorbed on clay. The second-order rate constant based on the concentration (mol g(-1)) of 1 per unit weight of clay was 2.7 +/- 0.1 mol(-1) s(-1) g for mica, which is appreciably lower than that for kaolin (23.9 +/- 0.4 mol(-1) s(-1) g). This difference can be explained by the localized adsorption of 1 on the surface for kaolin. However, the apparent turnover frequency ((kO(2))app/s(-1)) of 1 on mica was 2.2 times greater than on kaolin when the same fractional loading is compared. The higher cation exchange capacity (CEC) of mica statistically affords a shorter distance between the anionic sites to which 1 is attracted electrostatically, making the cooperative interaction between adsorbed molecules of 1 easier than that on kaolin. The higher CEC is important not only for attaining a higher loading but also for the higher catalytic activity of adsorbed 1.     

In situ observation of homogeneous nucleation of nanosized zeolite A

The formation of zeolite A (LTA) in the presence of tetramethylammonium cations is studied using in situ small angle and wide angle X-ray scattering (SAXS/WAXS) techniques. The SAXS measurements show the formation of homogeneous precursors 10 nm in size prior to the crystallization of LTA which were consumed during the crystallization. The crystal size is estimated by fitting the SAXS patterns with an equation for a cubic particle, and it is revealed that the final crystal size of the LTA depends on the synthesis temperature. However, although such temperature dependence is noted for the final crystal size, the initial precursor particles size appears to be closely similar (ca. 10 nm) irrespective of the synthesis temperature.     

Observation of multiple phase transitions in some even n-alkanes using a high resolution and super-sensitive DSC

The phase transitions of even n-alkanes, n-C₃₄H₇₀, n-C₃₆H₇₄, n-C₄₀H₈₂ and n-C₄₂H₈₆ with high purity have been measured using a high resolution and super-sensitive DSC. A new transition in the low temperature phase was observed in all the samples in the heating run. The surface freezing phenomenon was observed by thermal measurement for the first time in all the samples both in the heating and in the cooling run. The difference of the thermal behaviors between the heating and cooling run was also observed in all the samples.     

Single-chain magnet (NEt4)[Mn2(5-MeOsalen)2Fe(CN)6] Made of Mn(III)-Fe(III)-Mn(III) trinuclear single-molecule magnet with an S(T) = 9/2 spin ground state

The cyano-bridged trinuclear compound, (NEt(4))[Mn(2)(salmen)(2)(MeOH)(2)Fe(CN)(6)] (1) (salmen(2)(-) = rac-N,N'-(1-methylethylene)bis(salicylideneiminate)), reported previously by Miyasaka et al. (ref 19d) has been reinvestigated using combined ac and dc susceptibility measurements. The strong frequency dependence of the ac susceptibility and the slow relaxation of the magnetization show that 1 behaves as a single-molecule magnet with an S(T) = (9)/(2) spin ground state. Its relaxation time (tau) follows an Arrhenius law with tau(0) = 2.5 x 10(-)(7) s and Delta(eff)/k(B) = 14 K. Moreover, below 0.3 K, tau saturates around 470 s, indicating that quantum tunneling of the magnetization becomes the dominant process of relaxation. (NEt(4))[Mn(2) (5-MeOsalen)(2)Fe(CN)(6)] (2) (5-MeOsalen(2)(-) = N,N'-ethylenebis(5-methoxysalicylideneiminate)) is a heterometallic one-dimensional assembly made of the trinuclear [Mn(III)(SB)-NC-Fe(III)-CN-Mn(III)(SB)] (SB is a salen-type Schiff-base ligand) motif similar to 1. Compound 2 has two types of bridges, a cyano bridge (-NC-) and a biphenolate bridge (-(O)(2)-), connecting Mn(III) and Fe(III) ions and the two Mn(III) ions, respectively. Both bridges mediate ferromagnetic interactions, as shown by modeling the magnetic susceptibility above 10 K with g(av) = 2.03, J(Mn)(-)(Fe)/k(B) = +6.5 K, and J'/k(B) = +0.07 K, where J' is the exchange coupling between the trimer units. The dc magnetic measurements of a single crystal using micro-SQUID and Hall-probe magnetometers revealed a uniaxial anisotropy (D(T)/k(B) = -0.94 K) with an easy axis lying along the chain direction. Frequency dependence of the ac susceptibility and time dependence of the dc magnetization have been performed to study the slow relaxation of the magnetization. A mean relaxation time has been found, and its temperature dependence has been studied. Above 1.4 K, both magnetic susceptibility and relaxation time are in agreement with the dynamics described in the 1960s by R. J. Glauber for one-dimensional systems with ferromagnetically coupled Ising spins (tau(0) = 3.7 x 10(-)(10) s and Delta(1)/k(B) = 31 K). As expected, at lower temperatures below 1.4 K, the relaxation process is dominated by the finite-size chain effects (tau'(0) = 3 x 10(-)(8) s and Delta(2)/k(B) = 25 K). The detailed analysis of this single-chain magnet behavior and its two regimes is consistent with magnetic parameters independently estimated (J'and D(T)) and allows the determination of the average chain length of 60 nm (or 44 trimer units). This work illustrates nicely a new strategy to design single-chain magnets by coupling ferromagnetically single-molecule magnets in one dimension.     

Reactions of acetonitrile coordinated to a nitrosylruthenium complex with H2O or CH(3)OH under mild conditions: structural characterization of imido-type complexes

The reaction of cis-[Ru(NO)(CH(3)CN)(bpy)(2)](3+) (bpy = 2,2'-bipyridine) in H(2)O at room temperature proceeded to afford two new nitrosylruthenium complexes. These complexes have been identified as nitrosylruthenium complexes containing the N-bound methylcarboxyimidato ligand, cis-[Ru(NO)(NH=C(O)CH(3))(bpy)(2)](2+), and methylcarboxyimido acid ligand, cis-[Ru(NO)(NH=C(OH)CH(3))(bpy)(2)](3+), formed by an electrophilic reaction at the nitrile carbon of the acetonitrile coordinated to the ruthenium ion. The X-ray structure analysis on a single crystal obtained from CH(3)CN-H(2)O solution of cis-[Ru(NO)(NH=C(O)CH(3))(bpy)(2)](PF(6))(3) has been performed: C(22)H(20.5)N(6)O(2)P(2.5)F(15)Ru, orthorhombic, Pccn, a = 15.966(1) A, b = 31.839(1) A, c = 11.707(1) A, V = 5950.8(4) A(3), and Z = 8. The structural results revealed that the single crystal consisted of 1:1 mixture of cis-[Ru(NO)(NH=C(O)CH(3))(bpy)(2)](2+) and cis-[Ru(NO)(NH=C(OH)CH(3))(bpy)(2)](3+) and the structural formula of this single crystal was thus [Ru(NO)(NH=C(OH(0.5))CH(3))(bpy)(2)](PF(6))(2.5). The reaction of cis-[Ru(NO)(CH(3)CN)(bpy)(2)](3+) in dry CH(3)OH-CH(3)CN at room temperature afforded a nitrosylruthenium complex containing the methyl methylcarboxyimidate ligand, cis-[Ru(NO)(NH=C(OCH(3))CH(3))(bpy)(2)](3+). The structure has been determined by X-ray structure analysis: C(25)H(29)N(8)O(18)Cl(3)Ru, monoclinic, P2(1)/c, a = 13.129(1) A, b = 17.053(1) A, c = 15.711(1) A, beta = 90.876(5) degrees, V = 3517.3(4) A(3), and Z = 4.