A Bioinspired Gradient Design Strategy for Cellulose-Based Electromagnetic Wave Absorbing Structural Materials.

Cellulose nanofiber (CNF) possesses excellent intrinsic properties, and many CNF-based high-performance structural and functional materials have been developed recently. However, the coordination of the mechanical properties and functionality is still a considerable challenge. Here, a CNF-based structural material is developed by a bioinspired gradient structure design using hollow magnetite nanoparticles and the phosphorylation-modified CNF as building blocks, which simultaneously achieves a superior mechanical performance and electromagnetic wave absorption (EMA) ability. Benefiting from the gradient design, the flexural strength of the structural material reached ∼205 MPa. Meanwhile, gradient design improves impedance matching, contributing to the high EMA ability (-59.5 dB) and wide effective absorption width (5.20 GHz). Besides, a low coefficient of thermal expansion and stable storage modulus was demonstrated as the temperature changes. The excellent mechanical, thermal, and EMA performance exhibited great potential for application in stealth equipment and electromagnetic interference protecting electronic packaging materials.

Two Three-Dimensional LnIII Coordination Polymers Exhibiting Luminescent Sensing and a Magnetocaloric Effect.

Two lanthanide 3D coordination polymers [Ln2(L)4Cl2(H2O)4]n (Ln = Eu (1), Gd (2)) with quinoline-2-carboxylic acid (HL) as the ligand were successfully synthesized and characterized. Complex 1 exhibits a highly sensitive and selective luminescent response to 2,6-dipicolinic acid (DPA) in tap water and is virtually unaffected by interferences such as amino acids, aromatic carboxylic acids, and ions. With the addition of DPA, the luminescence intensity of complex 1 decreases rapidly to the naked eye. The detection limit of 1 toward DPA is 3.36 µM, which is much less than the infectious dose (60 µM) of the anthrax spores, indicating the high sensitivity of 1 to DPA. This study offers a basis for employing lanthanide complexes in real sample analysis, enabling direct and efficient detection of DPA with high sensitivity and specificity. Additionally, it is noteworthy that at a magnetic field strength of 7 T and a temperature of 3 K, the maximum entropy change for complex 2 attains a value of 23.56 J kg-1 K-1.

An All-Natural Wood-Inspired Aerogel.

The oriented pore structure of wood endows it with a variety of outstanding properties, among which the low thermal conductivity has attracted researchers to develop wood-like aerogels as excellent thermal insulation materials. However, the increasing demands of environmental protection have put forward new and strict requirements for the sustainability of aerogels. Here, we report an all-natural wood-inspired aerogel consisting of all-natural ingredients and develop a method to activate the surface-inert wood particles to construct the aerogel. The obtained wood-inspired aerogel has channel structure similar to that of natural wood, endowing it with superior thermal insulation properties to most existing commercial sponges. In addition, remarkable fire retardancy and complete biodegradability are integrated. With the above outstanding performances, this sustainable wood-inspired aerogel will be an ideal substitute for the existing commercial thermal insulation materials.

Di- and Tetranuclear Dysprosium Single-Molecule Magnets Bridged by Unprecedentedly Disassembled Nitrogen-Enriched Tetrazine Derivatives.

A series of di- and tetranuclear lanthanide complexes with the formulas [Dy2bmzch(tmhd)5 (CH3OH)]·CH3OH (1), [Dy2bmzch(dbm)4 (CH3O)(CH3OH)]·0.5CH3OH·0.5H2O (2), and Dy4bmzch(btfa)10 (3), where tmhd = 2,2,6,6-tetramethyl-3,5-heptanedionate, dbm = dibenzoylmethane, btfa = benzoyltrifluoroacetone, and bmzch = (Z)-N-[(E)-pyrimidin-2-ylmethylene]pyrimidine-2-carbohydrazonate, were structurally and magnetically characterized. More strikingly, although the nitrogen-enriched bridged ligand 3,6-di(pyrimidin-2-yl)-1,2,4,5-tetrazine (bmtz) was initially adopted, the structures of the complexes obtained indicated that bmtz underwent unprecedented asymmetric ring opening and generated a new ligand bmzch. Combined with different ß-diketonates, di- and tetranuclear dysprosium complexes were constructed in which the structural patterns are very sensitive to the selected ß-diketonates. In view of this, the bilateral and unilateral dinuclear Dy2 complexes 1 and 2 and tetranuclear Dy4 complex 3 were obtained by choosing different ß-diketonates. Magnetic test results reveal that both complexes 1 and 3 showcase typical slow magnetic relaxation behavior without an external direct-current field and the effective energy barrier of the latter is almost twice that of the former, while complex 2 only displays in-field single-molecule-magnetic behavior. Also of note is that these are the first tetrazine-type dysprosium-based single-molecule-magnets undergoing in situ asymmetric ring-opening reaction of this ligand that are formed.

Chloramphenicol-activated electro-chemiluminescent behavior of BNQDs-Ru(phen)32+ system for ultra-sensitive sensing of chloramphenicol in pharmaceutical and milk samples.

To improve the sensitivity for electro-chemiluminescent (ECL) detection of chloramphenicol (CAP), a common broad-spectrum antibiotic, boron nitride quantum dots (BNQDs) were prepared with excellent photoelectric property and low toxicity. After its structure and electrochemical property were investigated in detail, it was noted that the ECL signal of Ru(Phen)32+could be strengthened by the proposed BNQDs, which was further activated by ten's times in the presence of CAP. Under the optimized conditions, there was an excellent linear relationship between ΔECL and lgcCAPin a wide linear range from 1.0 × 10-10to 1.0 × 10-6mol l-1CAP. The detection limit was super-low to be 3.3 × 10-11mol l-1(S/N = 3). When applied for CAP detection in real pharmaceutical and food samples, the recoveries were between 97.8% and 105.7% with R.S.D. less than 3.3%. A possible CAP-activated ECL mechanism of BNQDs-Ru(phen)32+was also proposed. This work will offer a great potential for efficient monitoring of CAP pollution and clinical diagnosing of CAP-related diseases in future.

Chloramphenicol-activated electro-chemiluminescent behavior of BNQDs-Ru(phen)32+ system for ultra-sensitive sensing of chloramphenicol in pharmaceutical and milk samples.

To improve the sensitivity for electro-chemiluminescent (ECL) detection of chloramphenicol (CAP), a common broad-spectrum antibiotic, boron nitride quantum dots (BNQDs) were prepared with excellent photoelectric property and low toxicity. After its structure and electrochemical property were investigated in detail, it was noted that the ECL signal of Ru(Phen)32+ could be strengthened by the proposed BNQDs, which was further activated by ten's times in the presence of CAP. Under the optimized conditions, there was an excellent linear relationship between △ECL and lgcCAP in a wide linear range from 1.0×10-10 to 1.0×10-6 mol/L CAP. The detection limit was super-low to be 3.3×10-11 mol/L (S/N=3). When applied for CAP detection in real pharmaceutical and food samples, the recoveries were between 97.8 and 105.7 % with R.S.D. less than 3.3%. A possible CAP-activated ECL mechanism of BNQDs-Ru(phen)32+ was also proposed. This work will offer a great potential for efficient monitoring of CAP pollution and clinical diagnosing of CAP-related diseases in future.

One-dimensional nitrogen doped porous carbon nano-array arranged by carbon nanotubes for electrochemical sensing ascorbic acid, dopamine and uric acid simultaneously.

In this work, one-dimensional nitrogen doped porous carbon nano-arrays arranged by carbon nanotube (1D CNTs@NPC) were first constructed, using a coating technology at room temperature and followed by high temperature carbonization. It was expected that the resulting glassy carbon electrodes modified by 1D CNTs@NPC (CNTs@NPC/GCE) could express different electrochemical responses to ascorbic acid (AA), dopamine (DA), uric acid (UA), by virtue of the synergistic-improved effect between CNTs and NPC. Under the optimized conditions, there were excellent analytical parameters for CNTs@NPC/GCE to detect AA, DA and UA, i.e. a wide linear range of 40-2100µM for AA, 0.5-49µM for DA and 3-50µM for AA with low detection limits of 0.36µM, 0.02µmol l-1and 0.57µM respectively. Importantly, the proposed CNTs@NPC/GCE was efficiently applied to determine AA, DA and UA in some real samples with high stability, reproducibility and selectivity. This work will offer an efficient potential for diagnosing ascorbic acid, dopamine or uric acid-related diseases on clinical testing in future.

Joint Resource Allocation for Multiuser Opportunistic Beamforming Systems with OFDM-NOMA.

Opportunistic beamforming (OBF) is an effective technique to improve the spectrum efficiencies (SEs) of multiple-input-multiple-output (MIMO) systems, which can obtain multiuser diversity gains with both low computation complexity and feedback information. To serve multiple users simultaneously, many multiple-access schemes have been researched in OBF. However, for most of the multiple-access schemes, the SEs are not satisfactory. To further improve the SE, this paper proposes a downlink multiuser OBF system, where both orthogonal frequency division multiplexing (OFDM) and non-orthogonal multiple-access (NOMA) methods are applied. The closed-form expressions of the equivalent channels and SE are derived in frequency selective fading channels. Then, an optimization problem is formulated to maximize the SE, although the optimization problem is non-convex and hard to solve. To obtain the solution, we divide the optimization problem into two suboptimal issues, and then a joint iterative algorithm is applied. In the proposed optimization scheme, the subcarrier mapping ϑ, user pairing knc and allocated power Pknc are determined to maximize spectrum efficiency (SE) and reduce bit error ratio (BER). According to numerical results, the proposed method achieves approximately 5 dB gain on both SE and BER, compared to the existing beamforming methods with low feedback information. Moreover, the SE of the proposed method is approximately 2 (bps/Hz) higher than sparse code multiple-access (SCMA), when the number of waiting users and the ratio of transmit power to noise variance are respectively 10 and 20 dB. It is indicated that the proposed scheme can achieve high and low BER with the limited feedback and computation complexity, regardless of the transmit power and the number of waiting users.

Modulation of the Coordination Environment around the Magnetic Easy Axis Leads to Significant Magnetic Relaxations in a Series of 3d-4f Schiff Complexes.

A series of Salen-type Zn(II)-Dy(III) complexes [L1Zn(II)ClDy(III)(acac)2]·H2O (1), [L1Zn(II)BrDy(III)(acac)2]·H2O (2), [L1Zn(II)(H2O)Dy(III)(acac)2]·CH2Cl2·PF6 (3), [L2Zn(II)(H2O)Dy(III)(acac)2]·PF6 (4), and Co(III)-Dy(III) complexes [L1Co(III)Br2Dy(III)(acac)2]·CH2Cl2 (5), [L2Co(III)Cl2Dy(III)(acac)Cl(MeO)] (6), [L2Co(III)Cl2Dy(III)(acac)Cl(H2O)] (7), and [L2Co(III)Cl2Dy(III)(NO3)2(MeO)] (8) heterobinuclear single-molecule magnets (SMMs) were synthesized and magnetically characterized. These complexes were constructed by incorporating diamagnetic Zn(II) and Co(III) ions with acetylacetone (acac) and compartmental Schiff-base ligands (H2L1 = N, N'-bis(2-oxy-3-methoxybenzylidene)-1,2-phenylenediamine; H2L2 = N, N'-bis(2-oxy-3-methoxybenzylidene)-1,2-diaminocyclohexane). In the Zn(II)-Dy(III) (1-4) system, the coordination environments of the Dy(III) ions are nearly identical, but the apical coordination atom to the Zn(II) ion is different. Complexes 1, 2, and 4 displayed no magnetic relaxation in the absence of external magnetic field, but complex 3 displayed more pronounced SMM behavior with a relaxation energy barrier Ueff/ kB 38 K and magnetic hysteresis at 1.8 K. The SMM performances of 5, 6, and 7 were enhanced significantly by incorporating an octahedral Co(III) instead of square-pyramidal Zn(II) and replacing one of acac- group around Dy(III) ion by a neutral O atom, displaying Ueff of 167, 118, and 75 K as well as magnetic hysteresis up to 3.5 K. These studies indicated that the remote diamagnetic Zn(II) and Co(III) ions played a key role, and the SMM properties were very strongly related to the special coordination atoms configuration around Dy(III) ion. When this coordination configuration around was broken as 8 exhibited, however, it resulted in a dramatically decreased SMM performance. From this work, the key factors that significantly affect the SMM performance of these heteronuclear Zn(II)/Co(III)-Dy(III) SMMs are unambiguously presented.

Constructing high axiality mononuclear dysprosium molecular magnets via a regulation-of-co-ligands strategy.

Two lanthanide complexes with formulae [DyIII(LN5)(pentafluoro-PhO)3] (1) and [DyIII(LN5)(2,6-difluoro-PhO)2](BPh4) (2) (LN5 = 2,14-dimethyl-3,6,10,13,19-pentaazabicyclo[13.3.1]nonadecal (19),2,13,15,17-pentaene) were structurally and magnetically characterized. DyIII ions lie in the cavity of a five coordinate nitrogen macrocycle, and in combination with the introduction of multi-fluorinated monodentate phenoxyl coligands a high axiality coordination symmetry is built. Using the pentafluorophenol co-ligand, complex 1 with a D2d coordination environment, is obtained and displays moderate single-molecule magnets (SMMs) behavior. When difluorophenol co-ligands were used, a higher local axisymmetric pentagonal bipyramidal coordination geometry was observed in complex 2, which displays apparent slow magnetic relaxation behavior with a hysteresis temperature of up to 5 K. Further magnetic studies of diluted samples combined with ab initio calculations indicate that the high axiality plays a crucial role in suppressing quantum tunneling of magnetization (QTM) and consequently results in good slow magnetic relaxation behavior. Different fluoro-substituted phenoxyl co-ligands have phenoloxy oxygen atoms with different electrostatic potentials as well as a different number of phenoloxy coligands along the magnetic axis, resulting in different ligand field strengths and coordination symmetries.

Multifunctional lanthanide-based single-molecule magnets exhibiting luminescence thermometry and photochromic and ferroelectric properties.

Lanthanide-based single-molecule magnets (SMMs) have captivated the attention of researchers due to their great potential application in quantum information processing, storage, spintronics etc. Recent years have witnessed continuous breakthroughs in the field of SMMs, which make them very promising to be used in future practical functional applications. However, there remain formidable obstacles involving suppression of the quantum tunneling of magnetization (QTM) to maximize magnetic anisotropy, integrating and applying them in devices etc. Meanwhile, multifunctional 4f-based SMMs, which combine optical and electronic properties, are attracting increasing attention. This will provide a new perspective for future multifunctional device applications and deep insight into understanding the magnetic relaxation behavior as well. In this frontier article, we highlight the research that recently emerged involving 4f-based SMMs in combination with luminescence thermometry and photochromic and ferroelectric properties, respectively.

Ultrastrong, Thermally Stable, and Food-Safe Seaweed-Based Structural Material for Tableware.

Widely used disposable plastic tableware is usually buried or directly discharged into the natural environment after using, which poses potential threats to the natural environment and human health. To solve this problem, nondegradable plastic tableware needs to be replaced by tableware composed of biodegradable structural materials with both food safety and the excellent mechanical and thermal properties. Here, a food-safe sargassum cellulose nanofiber (SCNF) is extracted from common seaweed in an efficient and low energy consuming way under mild reaction conditions. Then, by assembling the SCNF into a dense bulk material, a strong sargassum cellulose nanofiber structural material (SCNSM) with high strength (283 MPa) and high thermal stability (>160 °C) can be prepared. The SCNSM also possesses good machinability, which can be processed into tableware with different shapes, e.g., knives and forks. The overall performance of the SCNSM-based tableware is better than commercial plastic, wood-based, and poly(lactic acid) tableware, which shows great application potential in the tableware field.

Nacre-Inspired Bacterial Cellulose/Mica Nanopaper with Excellent Mechanical and Electrical Insulating Properties by Biosynthesis.

The exploration of extreme environments has become necessary for understanding and changing nature. However, the development of functional materials suitable for extreme conditions is still insufficient. Herein, a kind of nacre-inspired bacterial cellulose (BC)/synthetic mica (S-Mica) nanopaper with excellent mechanical and electrical insulating properties that has excellent tolerance to extreme conditions is reported. Benefited from the nacre-inspired structure and the 3D network of BC, the nanopaper exhibits excellent mechanical properties, including high tensile strength (375 MPa), outstanding foldability, and bending fatigue resistance. In addition, S-Mica arranged in layers endows the nanopaper with remarkable dielectric strength (145.7 kV mm-1 ) and ultralong corona resistance life. Moreover, the nanopaper is highly resistant to alternating high and low temperatures, UV light, and atomic oxygen, making it an ideal candidate for extreme environment-resistant materials.

A salen-type trinuclear Zn2Gd complex.

In the trinuclear title complex, di-µ-acetato-1:2κ(2)O:O';2:3κ(2)O:O'-bis-{µ-6,6'-dimeth-oxy-2,2'-[cyclo-hexane-1,2-diylbis(methanylyl-idene)]diphenolato}-1:2κ(6)O(1),N,N',O(1'):O(6),O(6');2:3κ(6)O(6),O(6'):O(1),N,N',O(1')-2-gadolinium(III)-1,3-dizinc hexa-fluor-idophosphate methanol monosolvate monohydrate, [GdZn2(C22H24N2O4)2(CH3COO)2]PF6·CH3OH·H2O, the two Zn(II) ions are located in the inner N2O2 cavities of two 6,6'-dimeth-oxy-2,2'-[cyclo-hexane-1,2-diylbis(methanylyl-idene)]diphenolate (L) ligands. Both Zn(II) ions are five-coordinated by two O atoms and two N atoms from the L ligand and one O atom of an acetic acid mol-ecule, giving rise to a square-pyramidal geometry around the Zn(II) ions. The Gd(III) ion is nine-coordinated by four O atoms from the outer O2O2 sites of one ligand, and three O atoms from another ligand, in which there is one non-coordinating meth-oxy O atom. Two further O atom from different acetate ligands complete the nine-coordinate environment.

Schiff base tetranuclear Zn2Ln2 single-molecule magnets bridged by hydroxamic acid in association with near-infrared luminescence.

A series of Zn-Ln heteronuclear SMMs constructed by using a hexadentate compartment Schiff base Zn-precursor and lanthanoid ions were structurally and magnetically characterized, in which the two [Zn-Ln] moieties are bridged by a series of hydroxamic acids, resulting in double-decker tetranuclear complexes with the molecular formulae [ZnL1Ln(C2H5O)(qua)]2(CF3SO3)2·2C2H5OH ((1) Ln = Dy; (7) Ln = Yb), [ZnL1Ln(CH3O)(bnz)]2(CF3SO3)2·2CH3OH ((2) Ln = Dy), [ZnL1Ln(CH3O)(aca)]2(CF3SO3)2·2CH3OH ((3) Ln = Dy; (8) Ln = Yb), [ZnL2Dy(CH3O)(bnz)]2(CF3SO3)2·2CH3OH (4), [ZnL2Dy(CH3O)(aca)]2(CF3SO3)2·2CH3OH (5), and [ZnL3Dy(CH3O)(bnz)]2(CF3SO3)2·2CH3OH (6) (HL1 = N,N'-bis(2-hydroxy-3-methoxybenzylidene)-1,2-phenylenediamine, HL2 = N,N'-bis(2-hydroxy-3-methoxybenzylidene)-propane-1,2-diamine, HL3 = N,N'-bis(3-methoxysalicylidene)-1,3-propanediamine, qua = 2-quinolinecarboxylic acid, bnz = benzhydroxamic acid and aca = acetohydroxamic acid). Strikingly, the slow magnetic relaxation can be tuned by modifying the steric hindrance and/or electronic effect on the backbone of the Shiff base and the terminal substituents of hydroxamic acid, as well the magneto-structural correlations are studied. Furthermore, Yb congeners 7 and 8 were synthesized to explore dual-functional materials with both magnetic and fluorescence properties, and they displayed both slow magnetic relaxation and near-infrared (NIR) properties; the low temperature NIR spectroscopic data were correlated with the corresponding slow magnetic relaxation mechanism involving thermally activated ground states to the excited state.

Planar tetranuclear Dy(III) single-molecule magnet and its Sm(III), Gd(III), and Tb(III) analogues encapsulated by salen-type and ß-diketonate ligands.

The syntheses, structures, and magnetic properties are reported for four new lanthanide clusters [Sm(4)(µ(3)-OH)(2)L(2)(acac)(6)]·4H(2)O (1), [Gd(4)(µ(3)-OH)(2)L(2)(acac)(6)]·4CH(3)CN (2), and [Ln(4)(µ(3)-OH)(2)L(2)(acac)(6)]·2H(2)L·2CH(3)CN (3, Ln = Tb; 4, Ln = Dy) supported by salen-type (H(2)L = N,N'-bis(salicylidene)-1,2-cyclohexanediamine) and ß-diketonate (acac = acetylacetonate) ligands. The four clusters were confirmed to be essentially isomorphous by infrared spectroscopy and single-crystal X-ray diffraction. Their crystal structures reveal that the salen-type ligand provides a suitable tetradentate coordination pocket (N(2)O(2)) to encapsulate lanthanide(III) ions. Moreover, the planar Ln(4) core is bridged by two µ(3)-hydroxide, four phenoxide, and two ketonate oxygen atoms. Magnetic properties of all four compounds have been investigated using dc and ac susceptibility measurements. For 4, the static and dynamic data indicate that the Dy(4) complex exhibits slow relaxation of the magnetization below 5 K associated with single-molecule magnet behavior.

[Landscape pattern of built-up land in a typical mining city, Datong, Shanxi, China from 1986 to 2018.] / 1986­2018å¹´å ¸åž‹çŸ¿ä¸šåŸŽå¸‚å¤§åŒå¸‚å»ºè®¾ç”¨åœ°æ™¯è§‚æ ¼å±€.

Analyzing the landscape spatial layout and evolution characteristics of built-up land in a mining city is helpful to solve the environment problem, and can provide scientific basis for optimizing the urban land structure and taking timely intervention measures for transformation. Taking Datong, a typical mining city as the case, we examined the spatiotemporal characteristics of landscape of built-up land based on the spatial distribution data of built-up land from 1986 to 2018 with the landscape index analysis method, and detected the landscape change period with graphs obtained by Fourier transform and wavelet transform. The results showed that, during the study period, the area of built-up land in Datong City increased continually, with the growth rate gradually slowing down and the extent spreading from a "northeast-southwest" belt zone to the east. The fragmentation and complexity of the landscape pattern were increasing. The physical connectivity gradually decreased, while functional connectivity alternated between high and low values. The space expansion of Datong City and the fragmentation and complication of landscape pattern of its built-up land may all have a cycle of about 35 years, while the functional connectivity had a longer cycle than the physical connectivity.

[Altitudinal phenotypic plasticity of leaf characteristics of Polygonum viviparum]. / ç èŠ½è“¼å¶ç‰‡å¯¹æµ·æ‹”å˜åŒ–çš„è¡¨åž‹å¯å¡‘æ€§.

We investigated leaf tissue structure, leaf epidermis characteristics and chloroplast ultrastructure of Polygonum viviparum at different altitudes (2300, 3200 and 3900 m) on the Qilian Mountain, using paraffin section, scanning electron microscopy and transmission electron microscopy methods. The results showed that plant leaves were typical bifacial. With increasing altitude, the number of leaf epidermal hair reduced but the diameter of hair increased, with more compact of the cuticular wax layer on leaf lower epidermis. Leaf thickness reached a maximum at 3200 m and was increased by 39.6% and 50.5%, respectively, compared with that from 2300 m and 3900 m. From 2300 m to 3200 m, the cell layers of palisade tissue increased from two to three, while intercellular space decreased. The cell layer of spongy tissue did not change, whereas intercellular space increased with increasing altitude. At 3900 m, the number of cell layer of palisade tissue reduced to two, epidermal cell volume and the intercellular space of palisade tissue increased while the intercellular space of spongy tissue decreased. The thickness of epidermal cell increased. There was no significant difference among three altitudes in the number of cell layers. The accumulation of surface appurtenances and the substomatal appendages, and stomata density of lower epidermis increased with altitude. Meanwhile, the position of stomata changed from arched epidermis to invagination. From 2300 m to 3200 m, the grana lamella increased from 6-9 to 8-12 and then reduced to 2-3 at 3900 m. The number of grana decreased, the lamellae became dense, the arrangement direction of grana was irregular at 3900 m. The chloroplasts swelling and the envelope partially degradation could be observed. The correlations among the anatomical characteristics of leaves indicated an apparent co-evolution between parts of anatomical indices in the leaves. In particular, indices such as spongy tissue thickness exhibited high plasticity across altitudes. Our results suggested that diffe-rences in anatomical structure and ultrastructure characteristics of P. viviparum along altitude were adaptation strategies for the complicated alpine heterogeneous habitats.

Anomeric configuration-dependence of the Lattrell-Dax epimerization from D-glucose to synthetically useful D-allose derivatives.

D-Allose and its derivatives play important roles in the field of health care and food nutrition. Pure and well-defined D-allose derivatives can facilitate the elucidation of their structure-activity relationship as an essential step for drug design. The Lattrell-Dax epimerization, refers to the triflate inversion using nitrite reagent, is known as valuable method for the synthesis of rare D-allose derivatives. Here, the influence of protecting group patterns on the transformation efficiency of D-glucose derivatives into synthetically useful D-alloses and D-allosamines via the Lattrell-Dax epimerization was studied. For C3 epimerization of D-glucose derivatives bearing O2-acyl group, an anomeric configuration-dependent acyl migration from O2 to O3 was found. In addition, a neighbouring group participation effect-mediated SN1 nucleophilic substitution of the D-glucosamine bearing C2 trichloroacetamido (TCA) group in the Lattrell-Dax epimerization was dependent upon anomeric configuration. Thus, the effect of anomeric configuration on the Lattrell-Dax epimerization of D-glucose suggests that ß-D-glucosides with low steric hindrance at C2 should be better substrates for the synthesis of D-allose derivatives. Significantly, the efficient synthesis of the orthogonally protected D-allose 13 and D-allosamine 18 will serve well for further assembly of complex glycans.

(Acetone-2κO){µ-6,6'-dimeth-oxy-2,2'-[propane-1,2-diylbis(nitrilo-methyl-idyne)]diphenolato-κ1:2O,O,O,O:O,N,N',O}tris(nitrato-1κO,O')copper(II)terbium(III).

In the title heteronuclear complex, [CuTb(C(19)H(20)N(2)O(4))(NO(3))(3)(CH(3)COCH(3))], the Cu(II) ion is five-coordinated by two O and two N atoms from the 6,6'-dimeth-oxy-2,2'-[propane-1,2-diylbis(nitrilo-methyl-idyne)]diphenolate ligand (L) and an O atom from the acetone mol-ecule in a square-pyramidal geometry. The Tb(III) ion is ten-coordinated by six O atoms from three chelating nitrate ligands and four O atoms from the L ligand. In L, the CH(2)-CH-CH(3) fragment is disordered over two conformations, with refined occupancies of 0.725 (11) and 0.275 (11).