Syntheses and Structural Characterization of 1D Coordination Polymers of Transition‐Metal Atoms Containing 2,4‐Pyridinedicarboxylate Bridges

By employing one bridging ligand, 2,4‐pyridinedicarboxylate (2,4‐pda^2?), three one‐dimensional (1D) coordination polymers of [Cu(2,4‐pda)(H₂O)₂]_∞ ( 1 ), {[Cu₄(2,4‐pda)₄(H₂O)₈]·3H₂O}_∞ ( 2 ), and {[Cd(2,4‐pda)(H₂O)₃]·H₂O}_∞ ( 3 ) were synthesized. A simple zigzag polymeric chain is observed for both 1 and 3 , but a railroad‐like zigzag polymeric chain is observed for 2. Almost all water molecules, whether coordinated or not, are involved in hydrogen bonding interactions and help to tie up the 1D polymeric chains of 1‐3 into a three‐dimensional (3D) network. A comparison about the coordination geometries in all similar coordination polymers available to date is also included.     

Zn2+@Polyvinylpyrrolidone and Urushiol Preparation of Nanofibrous Membranes and Their Synergistic Effect

In this study, lacquer is gathered from a lacquer tree and rotary evaporation is used to remove impurities to obtain urushiol. Next, 10 mL of anhydrous ethanol serves as the solvent for blending polyvinylpyrrolidone (PVP) at a specified content (0.7 g and 0.2–0.7 g urushiol) to form an electrospinning solution. Electrospinning is carried out with a voltage of 18 kV to prepare PVP/urushiol nanofibrous membranes. At a ratio of 7/4, the PVP/urushiol nanofibrous membranes are not eroded in 98% sulfuric acid and these membranes also demonstrate a 50–60% antibacterial effect against Staphylococcus aureus and Escherichia coli. Moreover, the antibacterial effect can be boosted to 98% with the incorporation of zinc ions. The results indicate that anhydrous ethanol can remove the sensitization of urushiol from PVP/urushiol membranes. Furthermore, animal test results indicate that when rats are in contact with PVP/urushiol anhydrous ethanol for 48 h, their skins are free from dark brown skin allergy. The presence of PVP eliminates the sensitization of urushiol, and the nanofibrous membranes demonstrate low toxicity. Hence, urushiol is the only natural material that enables PVP to withstand 98% sulfuric acid as well as acquire hydrolyzability, thereby qualify PVP as a medical material.     

Accelerated direct electrochemistry of hemoglobin based on hemoglobin-carbon nanotube (Hb-CNT) assembly

In this study, we have demonstrated that hemoglobin can be coupled to acid-treated multiwall carbon nanotubes in the presence of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) and assembled as hemoglobin-carbon nanotube (Hb-CNT) composites. Our observations of the electrochemical studies demonstrate that the electrochemical response of Hb-CNT assembled in the presence of EDC is much higher than that in the absence of EDC. It is evident that the direct electron transfer of hemoglobin could be effectively accelerated in the Hb-CNT assembly by using EDC on a glassy carbon electrode (GCE), and the relative electron transfer rate constant K(s) is found to be 1.02+/-0.05 s(-1). The results of our studies illustrate that the assembly of hemoglobin-multiwall carbon nanotubes using EDC could provide a novel strategy to effectively facilitate the direct electrochemistry of heme-containing proteins, which could be further utilized as a promising biosensor for some specific biological substrate and related biological process.     

Selective Determination of Vitamin B2 at Electrochemically Activated Glassy Carbon Electrode

Electrochemically activated glassy carbon electrodes were applied to the preconcentration and electroanalysis of Vitamin B₂ (VB₂) in multivitamin preparation. Voltammetric peak currents showed linear response for VB₂ concentrations in the range between 0.1 to 3.0 M with a large slope of 12.2 AM^-1 and a correlation coefficient of 0.996. The reproducibility of the voltammetric measurements was usually less than 7% RSD for five replicate measurements. Common vitamin and metal species did not interfere the determination.     

A novel electrochemical approach for fabrication of photoluminescent erbium-doped porous silicon

21 /cm³. After this new ECD treatment, PS:Er was found to emit much more intense room-temperature visible photoluminescence than both the porous silicon control and the PS:Er prepared by constant-current ECD. Room-temperature IR photoluminescence around 1.54 μm was observed for the first time without any post-doping annealing. Received: 3 September 1998/Accepted: 9 September 1998     

Massive transfer of vertically aligned Si nanowire array onto alien substrates and their characteristics

Si nanowires (NWs) are promising materials for future electronic, photovoltaic, and sensor applications. So far the Si NWs are mainly formed on particular substrates or at high temperatures, greatly limiting their application flexibility. Here we report a low temperature process for forming and massively transferring vertically aligned Si NWs on alien substrates with a large density of about (3-5) × 10⁷ NWs/mm². The X-ray diffraction spectrum reveals that the transferred NWs exhibit almost the same crystal property as the bulk Si. Our investigation further shows that the transferred NWs have exceptional optical characteristics. The transferred Si NWs of 12.14 μm exhibit the transmittance as low as 0.3% in the near infrared region and 0.07% in the visible region. The extracted absorption coefficient of Si NWs in the near infrared region is about 3 × 10³ cm⁻¹, over 30 times larger than that of the bulk Si. Because of the low temperature process, it enables a large variety of alien substrates such as glass and plastics to be used. In addition, the exceptional properties of the transferred NWs offer potential applications for photovoltaic, photo-detectors, sensors, and flexible electronics.     

Super-edge-graceful Labelings of Some Cubic Graphs

The notion of super-edge-graceful graphs was introduced by Mitchem and Simoson in 1994.However, few examples except trees are known. In this paper, we exhibit two classes of infinitely many cubic graphs which are super-edge-graceful. A conjecture is proposed.     

Residue races

Given a prime p and distinct non-zero integers a₁, a₂,..., a_k (mod p), we investigate the number N = N(a₁, a₂,..., a_k; p) of residues n (mod p) for which (na₁)_p < (na₂)_p < ... < (na_k)_p, where (b)_p is the least non-negative residue of b (mod p). We give complete solutions to the problem when k = 2,3,4, and establish some general results corresponding to k≥5. The first author is a Presidential Faculty Fellow. He is also supported, in part, by the National Science Foundation. 2000 Mathematics Subject Classification Primary—11A07; Secondary—11F20     

A Correlated Digital Sum Problem Associated with Sums of Three Squares

Let (n) be the error term associated with the asymptotic formulafor the counting function on the set of numbers that are sumsof three squares. By considering (n) as a correlated digitalsum and applying the method of H. Delange on ordinary digitalsums we give very precise information on the average value of(n) in terms of a periodic continuous nowhere differentiablefunction having an absolutely convergent Fourier series withcoefficients expressed in terms of the Hurwitz zeta function.