Ultraviolet difference spectroscopic study on the interactions of cellulase fromTrichoderma reesei with cellodextrins

The formation of cellodextrin-cellobiohydrolase complex was studied by ultraviolet difference spectroscopy. Upon the binding of cellodextrins (G₇‐G₃), cellobiohydrolase (EC 3.2.1.91) purified fromTrichoderma reesei produced difference spectra having maxima at 289‐293 nm and 283‐286 nm. These spectra are consistent with prior observations reported for lysozyme and amylase. In this case, water soluble cellulose oligomers (i.e., cellodextrins) are shown to interact with tryptophan residue(s) on cellobiohydrolase. The difference spectral maxima observed at acidic or alkaline pH were shifted. This was accompanied by a marked decrease of binding ability of cellobiohydrolase for cellodextrins. The standard free energy change for the association of cellodextrins to the cellobiohydrolase was an order of 4 kcal/gmol. The association constant of enzyme for substrate decreases by 15‐20% as temperature increases from 20 to 48°C. At 25°C, the dissociation constants for the enzyme with respect to cellohexose and cellotriose were estimated to be 1.19 and 1.37 mM, respectively. A decrease in dissociation constants was observed with an increase in the number of glucosyl units from 3 to 6. This suggests that there may be six or more subsites in the active center of cellobiohydrolase.     

High-resolution proton nuclear magnetic resonance studies of urine from asphyxiated newborn infants

High-resolution proton nuclear magnetic resonance spectroscopy was used to study human urine obtained from 10 normal babies and twenty babies with various degrees of neonatal asphyxia, respiratory distress syndrome (RDS), and meconium aspiration syndrome (MAS). All sick babies showed different degrees of oxygen deficiency, indicated by an obvious increase of the lactate signal level in the urine spectra. Changes in the concentration of other urinary metabolites produced from the citric acid cycle were also observed. In extremely serious cases, the signals of some of the major components, including citrate, α-ketoglutarate, and succinate, simply disappeared. The spectra of urine, serum, and CSF of an infant suffering from SIDS showed common characteristics of the metabolites.     

Effects of Ligand Chain Length and Terminal N-Alkylation on the Protonation Constants and Stability Constants of Some Transition Metal Complexes of Linear Tetraaza and Pentaaza Ligands

A number of terminal N-alkylated linear tetraaza and pentaaza ligands were prepared. Their ligand protonation constants and some transition and post-transition metal (Ni²⁺, Cu²⁺, Zn²⁺, and Cd²⁺) complex stability constants were determined by potentiometric titration methods. In general, methylation and ethylation at the terminal nitrogen atoms caused the corresponding ligand nitrogen basicity to increase; however, the corresponding metal complex stabilities were decreased compared to the non-alkylated structural analogs, presumably due to a steric effect.     

Theoretical Studies of Distyrylbenzene and its Optical Properties

The electronic and geometrical properties of distyrylbenzene (DSB) are investigated by using chemistry theoretical calculation methods. Specifically, the excited state properties are studied by performing ab initio correlation interaction singlet (CIS) and time‐dependent density functional theory; the ground state and Raman activities are computed by density functional theory with the B3LYP method. Eight conformers of distyrylbenzene are found and they are derived from three isomers which are cis, cis‐, cis, trans‐, and trans, trans‐, respectively. The relative energy shows that each isomer of three types is separated with a large energy barrier, but a small energy difference of each conformer is found if they are in the same type. The transition state also shows the barrier between conformers is lower than isomers. The computed excited transition energies using ZINDO/S based on the optimized geometries at a DFT/B3LYP level with 6–31+G show an excellent agreement with experimental absorption spectra.     

Syntheses of oxazabicycle library via one-pot tandem reactions

A practical protocol for the preparation of a parallel solution-phase library of oxazabicycle is reported. Target compounds were obtained in moderate to good yields by a Yb(OTf)3-catalyzed one-pot tandem reaction from various anisidines, aromatic aldehydes, isobutyraldehyde, and 4-hydroxycoumarins/dimedone. Purification of the final products by either recrystallization in ethyl acetate/methylene chloride or column chromatography allowed easy isolation of the 18 components of the array.     

MAC-level Forward Error Correction mechanism for minimum error recovery overhead and retransmission

Wireless transmission suffers from poor wireless channel conditions, such as high bit error rate and error bursts resulting from channel fading and radio interference. The MAC-level Forward Error Correction (MFEC) mechanism is proposed to solve these problems. The MFEC mechanism cannot only adaptively adjust Forward Error Correction (FEC) redundancy, depending on the network condition, but can also retransmit whole packets even if the error packet includes several bit errors. In this paper, an Adaptive MAC-level FEC (AMFEC) mechanism is proposed to improve wireless transmission quality. The AMFEC mechanism relies on the effective packet loss rate model to dynamically adjust MFEC redundancy in order to minimize error recovery overhead. The AMFEC mechanism will retransmit the error of sub-packets and increase FEC redundancy to reduce transmission redundancy. The AMFEC mechanism not only enhances the quality of wireless transmission but also reduces the overhead of retransmission. The experimental results show the AMFEC mechanism is better than conventional MFEC mechanisms.     

The inverse problem for differential pencils on a star-shaped graph with mixed spectral data

The partial inverse problem for differential pencils on a star-shaped graph is studied from mixed spectral data.More precisely,we show that if the potentials on all edges on the star-shaped graph but one are known a priori then the unknown potential on the remaining edge can be uniquely determined by partial information on the potential and a part of eigenvalues.     

Challenges in quantum dot-neuron active interfacing

Semiconductor nanocrystal quantum dots (qdots) are now being explored in applications requiring active cellular interfaces, such as biosensing and therapeutics in which information is passed from the qdot to the biological system, or vice versa, to perform a function. These applications may require surface coating chemistry that is different from what is commonly employed for passive interface applications like labeling (i.e., thick polymer coatings such as poly(ethylene glycol) (PEG)), in which the only concern is nonspecific sticking to cells and biocompatibility. The thick insulating coatings that are generally needed for labeling are generally not suitable for active qdot-cell interface applications. There is currently little data regarding the interactions between viable cells and qdots under physiological conditions. Our initial investigations using mercaptoacetic acid-coated CdS and CdTe qdots as a simple model to interface with neuron cell surface receptors under physiological conditions uncovered two significant technological hurdles: nonspecific binding and endocytosis. Nonspecific binding can be extensive and in general there appears to be greater nonspecific binding for larger particle sizes, but this also depends sensitively on the particle surface characteristics and the type of neuron, possibly indicating a detailed relationship between particle-cell affinity and cell membrane chemistry. More importantly, qdot endocytosis occurs rapidly at physiological temperature for the different nerve cell types studied, within the first five minutes of exposure to both CdS and CdTe qdots, regardless of whether the molecular coatings specifically recognize cell surface receptors or not. As a consequence, new strategies for tagging cell surface recognition groups for long-term active interfacing with cells under physiological conditions are needed, which requires more sophisticated ligands than MAA but also the absence of thick insulating coatings.     

Dispersion relations of the surface plasma oscillations of multilayers

An equation for determining the dispersion relations of the surface plasma oscillations has been derived for the most general case of multilayers. The equation is given in a very simple form of the vanishing of the trace of a product of 2×2 matrices of recursive type.