Long‐Chain Branching with Metallocene Catalysts: Is a Purely Kinetic Mechanism for Terminal Branching Sufficient?

Rate constants for long‐chain branch formation during ethylene polymerization with metallocene catalysts were estimated and compared to polymerization rate constants for long α‐olefins. Unexpectedly, these branching constants were found to be comparable to the reactivity ratios of much shorter α‐olefins. Micromixing effects or a parallel mechanism for long‐chain branch generation are proposed as possible explanations for this finding.

Comparison between the α‐olefin and branching incorporation rate constants, normalized by the propagation rate constant (the values estimated from ref. 1 are subject to a significant uncertainty because the reaction conditions are not provided. A 10 wt.‐% polymer fraction in the reactor was assumed to estimate these values).     

Improved Livingness and Control over Branching in RAFT Polymerization of Acrylates: Could Microflow Synthesis Make the Difference?

The superior capabilities of structured microreactors over batch reactors are demonstrated for reversible addition–fragmentation chain transfer (RAFT) solution polymerization of n‐butyl acrylate with the aid of simulations, explicitly accounting for the chain length distribution of all macrospecies types. Since perfect isothermicity can be established in a microreactor, less side products due to backbiting and β‐scission are formed compared to the batch operation in which ineffective heat removal leads to an undesirable temperature spike. For a given RAFT chain transfer agent (CTA), additional microstructural control results under microflow conditions by optimizing the reaction temperature, lowering the dilution degree, or decreasing the initial molar ratio of monomer to RAFT CTA.

     

A Phaseolus vulgaris Leukoagglutinin Biosensor as a Selective Device for the Detection of Cancer-associated N-glycans with Increased β1→6 Branching

A Phaseolus vulgaris leukoagglutinin (PHA−L) impedimetric biosensor was developed for the selective detection of cancer-associated N-glycans presenting increased β1→6 GlcNAc branching. The increase in the biosensor‘s impedance after sample incubation was indicative of lectin recognition and complex formation between PHA−L and N-glycans with increased β1→6 GlcNAc branching, present in serum glycoproteins. Bovine thyroglobulin was used as a model glycoprotein and a linear correlation was found between glycoprotein concentration and analytical signal from 0.05 to 2.0 mg ml⁻¹. The biosensor was validated by analyzing serum samples from patients with diverse types of carcinomas.     

Ab initio Study of the Potential Energy Surface and Product Branching Ratios for Reaction of O（^1D） with C2H5CI

The potential energy surface of O（^1D）＋C2H5Cl reaction was studied using QCISD（T）/6- 311＋＋G（d,p）//MP2/6-31G（d,p） method. The calculations reveal an insertion-elimination mechanism. The insertion reaction of O（^1D） and C2H5Cl produces two energy-rich intermediates, IM1 and IM2, which subsequently decompose into various products. The calculations of the branching ratios of various products formed through the two intermediates were carried out using RRKM （Rice-Ramsperger-Kassel-Marcus） theory at the collision energies of 0, 20.9, 41.8, 62.7, 83.6, 104.5, and 125.4 kJ/mol. HCl is the main decomposition product for IM1; CH2OH is the main decomposition product for IM2. Since IM1 is more stable than IM2, HCl is probably the main product of the O（^1D）＋C2H5Cl reaction.     

Long Chain Fatty Acid Affects Excited State Branching in Bilirubin-Human Serum Protein Complex?

After binding to human serum albumin, bilirubin could undergo photo-isomerization and photo-induced cyclization process. The latter process would result the formation of a product, named as lumirubin. These photo induced behaviors are the fundamental of clinical therapy for neonatal jaundice. Previous studies have reported that the addition of long chain fatty acids is beneficial to the generation of lumirubin, yet no kinetic study has revealed the mechanism behind. In this study, how palmitic acid affects the photochemical reaction process of bilirubin in Human serum albumin (HSA) is studied by using femtosecond transient absorption and fluorescence up-conversion techniques. With the addition of palmitic acid, the excited population of bilirubin prefers to return to its hot ground state (S₀) through a 4 ps decay channel rather than the intrinsic ultrafast decay pathways (< 1 ps). This effect prompts the Z-Z to E-Z isomerization at the S$_0$ state and then further increases the production yield of lumirubin. This is the first time to characterize the promoting effect of long chain fatty acid in the process of phototherapy with femtosecond time resolution spectroscopy and the results can provide useful information to benefit the relevant clinical study.     

Pointing the way to the products? Comparison of the stress tensor and the second-derivative tensor of the electron density

The eigenvectors of the electronic stress tensor can be used to identify where new bond paths form in a chemical reaction. In cases where the eigenvectors of the stress tensor are not available, the gradient-expansion-approximation suggests using the eigenvalues of the second derivative tensor of the electron density instead; this approximation can be made quantitatively accurate by scaling and shifting the second-derivative tensor, but it has a weaker physical basis and less predictive power for chemical reactivity than the stress tensor. These tools provide an extension of the quantum theory of atoms and molecules from the characterization of molecular electronic structure to the prediction of chemical reactivity.     

Is the ion-linear quadrupole capture rate constant anisotropic with respect to the sign of the product of the charge on the ion and the quadrupole moment of the molecule?

The sign of the charge-quadrupole moment product is shown to affect the rate of ion-linear quadrupole capture.

---

- .

     

Is the dynamical polarization a significant part of the contribution of the triples to the correlation energy?

One may call dynamical polarization of doubly excited configurations the energy lowering of these configurations under the response of the other electrons to the so-created fluctuation of the electric field. This contribution of triply excited configurations may be identified and calculated through a computation that only requires a computation time proportional to the sixth power of the number of molecular orbitals (MOs), instead of the seventh power for the total contribution of the triples. Its amplitude depends on the choice of the MOs and becomes important when localized MOs are used.     

Does the Temperature of the prise de mousse Affect the Effervescence and the Foam of Sparkling Wines?

The persistence of effervescence and foam collar during a Champagne or sparkling wine tasting constitute one, among others, specific consumer preference for these products. Many different factors related to the product or to the tasting conditions might influence their behavior in the glass. However, the underlying factor behind the fizziness of these wines involves a second in-bottle alcoholic fermentation, also well known as the prise de mousse. The aim of this study was to assess whether a low temperature (13 °C) or a high temperature (20 °C) during the in-bottle fermentation might have an impact on the effervescence and the foaming properties (i.e., collar height and bubble size) of three French sparkling wines (a Crémant de Loire and two Champagne wines), under standard tasting conditions. Our results showed that sparkling wines elaborated at 13 °C and served in standard tasting conditions (i.e., 100 mL, 18 °C) had better ability to keep the dissolved CO₂ (between 0.09 and 0.30 g/L) in the liquid phase than those elaborated at 20 °C (with P < 0.05). Most interestingly, we also observed, for the Crémant de Loire and for one Champagne wine, that the lower the temperature of the prise de mousse, the smaller (with P < 0.05) the bubbles in the foam collar throughout the wine tasting.     

Correlation Analysis of the Runoff of the Rivers and the Seisms in China

In recent hundred years the annual discharge variations of the Changjiang River (represented by the Yichang station) and the Huanghe River (represented by Shanxian and Tangnaihe, respectively) have closely related to the geographical distribution of the earthquakes coming about in China in the same year, Both the occurrence of the destructive seism or seismic swarm in the river basins and the disappearance of the shocks in the east and south of the basins are the conditions that the Changjiang and Huanghe Rivers are the high flow while that the strong earthquake of magnitude 7 or more occurred in North China is the condition for the Changjiang low flow year and that of 6 or more in the Qilian Mountains area is for the Huanghe River. In the latter part of this paper, a 2-year sample is given to explain that the conditions of the 2 rivers being high flow years are that the north-south seismic belt is active and in the meanwhile no seism occurred in South China, and those of the low flow year are that the     

Micellar Copolymerization: the State of the Arts

Over the past two decades, hydrophobically modified water-soluble polymers (HMWSPs), particularly hydrophobically associating polyacrylamides (HAPAMs), have attracted increased interest owing to their practical and fundamental importance[1]. This system usually consists of a hydrophilic backbone with a small proportion (generally less than 2 mol %) of hydrophobic pendent groups. When dissolved in aqueous solutions, the apolar moieties tend to exclude water and are held together by intra- a…     

Self-sorting: the exception or the rule?

In this paper, we pose the question of whether self-sorting in designed systems is exceptional behavior or whether it is likely to become a more general phenomenon governing molecular recognition and self-assembly. To address this question we prepared a mixture comprising two of Davis' self-assembled ionophores, Rebek's tennis ball and calixarene tetraurea capsule, Meijer's ureidopyrimidinone, Reinhoudt's calixarene bis(rosette), and two molecular clips in CDCl(3) solution and observed the behavior of this ensemble by (1)H NMR. As hypothesized, high-fidelity self-sorting behavior was observed. The influence of several key variables-temperature, concentration, equilibrium constants, and the presence of competitors-on the fidelity of self-sorting is described. These results show that self-sorting is neither the exception nor the rule. They suggest, however, that the subset of known molecular aggregates that exceed the criteria required for thermodynamic self-sorting is larger than previously appreciated and potentially quite broad.     

Noninvasive Detection of the Gases Inside the Sealed Batteries by the On-line Mass Spectrometry

Mass spectrometer is connected through an adaptor to a sealed small battery to probe the gas phase changes inside the battery. The factors influencing the response time are analyzed with a simplified model. The feasibility of the new technique is demonstrated with a Ni-Cd battery, showing different profiles of MS intensities for O2 and H2. Compared with gas chromatography, this technique has the advantage of being noninvasive and should be useful for the study and diagnostic examination of small sealed batteries.     

Exploration on the Biotechnological Aspect of the Ureolytic Bacteria for the Production of the Cementitious Materials—a Review

Biomineralization is a process that leads to the formation of minerals using the biologically or biotechnologically mediated route. Calcium carbonate is one such biomineral that is secreted by the ureolytic bacteria which contributes for the strengthening and improvement of cementitious and sandy materials. It is a new and innovative area in the geotechnological engineering and structural engineering due to its wide range of implications in strengthening of soil, sand, stone, and cementitious materials. The shape and size of the calcium carbonate particle vary with the strain of the bacterium used, and it is species specific. This paper aims in the critical review of the mechanism of calcium carbonate precipitation by the bacterium, various bacteria involved, and the useful outputs of the technique of biomineralization. Based on the critical review, it also recommends the future development and research in the field to develop a technology that can strengthen the existing and the proposed structures.     

Synthesis of two peptides of α-bungarotoxin and the participation of the amino acid residue Trp-28 of the neurotoxin in the antigenicity of the molecule

Using the method of solid-phase peptide synthesis, two peptides have been synthesized, one of which corresponds to the central ring structure of -bungarotoxin (-BTX), while the second has in position 28 a Gly residue in place of the Trp in the first peptide, and their interrelationship with antitoxin antibodies has been investigated. It has been shown that the amino acid residue Trp-28 of -BTX, which is the contact residue in binding with the acetylcholine receptor, also participates directly in binding with the active centers of antibodies to -BTX.Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 628–631, July–August, 1997.     

Effect of the Composition of the Water–Dimethyl Sulfoxide Solvent on the Thermodynamics of the Formation of the [Ag(18-Crown-6)]+Complex

The effect of a water–dimethyl sulfoxide solvent (X _DMSO= 0–0.97, where X _DMSOis the mole fraction of DMSO) on the thermodynamics of complexation between Ag⁺and 18-crown-6 and the solvation of all reagents involved in this equilibrium were studied. In aqueous solutions, the complex is stable mainly because of the enthalpy contribution to _r G°. For X _DMSO> 0.3, the contributions from entropy and enthalpy become comparable in magnitude, but they are opposite in sign. In the binary solvent, the complex is most stable at X _DMSO= 0.2 to 0.3. Analysis of the enthalpy characteristics of reagent solvation showed that this solvent effect was due to the superposition of two opposite solvation contributions occurring with an increase in the DMSO concentration in the binary solvent, namely, the destabilization of the ligand solvate sphere and the formation of stable Ag⁺complexes with DMSO.     

Preface for the Special Column of the INRET 2006

I would like to take this opportunity to thank the editorial board of Journal of Natural Gas Chemistry for allowing me to write a preface for this special column. The articles appearing in this section are specially selected from the First International Conference on Natural Resources Engineering and Technology 2006 （INRET 2006）. In line with the theme of JNGC, the selected articles are focused on natural gas or low hydrocarbon conversions to important chemicals, fuels and materials. The conference was held on July 24-25, 2006 in Marriott Putrajaya, Malaysia. It was organized by the Chemical and Biotechnology （ChemBio） Focus Group, under the Research Management Centre, Universiti Teknologi Malaysia.     

Studies of the dissociation and the protonation of TB-chlorosulphophenol

The dissociation constant of each step for TB-chlorosulphophenol has been determined by potentiometric method, and the thermodynamic constants, △G°, △H° and △S°, of the dissociation process have been calculated. The protonation constants were measured by the spectrophotometric method. The pH values of various forms of anions of the chromogenic reagent at their concentrations were also calculated.     

Does the topological approach characterize the hydrogen bond?

 The topological analysis of the electron localization function has been applied to complexes representative of the weak, medium and strong hydrogen bond. For both the weak and the medium hydrogen bonds, the number of basins in the complexes is the sum of those of the moieties. In this case, the formation of a weak or a medium hydrogen-bonded complex does not involve a chemical reaction. In the weak hydrogen bond case, the reduction of the localization domain yields two domains in the first step, which can be partitioned afterwards into valence and core domains. In contrast, for medium complexes the core–valence separation is the first event which occurs during the reduction process and therefore the complex should be considered as a single molecular species. Moreover, the analysis of the basin population variance indicates in this case a noticeable delocalization between the V(A, H) and V(B) basins. Finally, the symmetrical strong hydrogen bond has a protonated basin V(H) at the bond midpoint. Such a topology corresponds to an incomplete proton transfer and to a rather covalent bond. Received: 19 April 1999 / Accepted: 22 July 1999 / Published online: 17 January 2000