Effect of test temperature on separation number

The separation number is affected by a variety of extra-column factors (e.g. the injection process, the nature of the sample, and plumbing defects in the inlet and detector) as well as factors related to column efficiency. The magnitude of the separation number, as affected by the column, varies inversely with column temperature and directly with the partition ratios of the test compounds. The interrelationships of column temperature and partition ratios are explored.     

“Bicarburet of Hydrogen”. Reappraisal of the Discovery of Benzene in 1825 with the Analytical Methods of 1968

The historical background and the admirable analytical procedure that led Michael Faraday to the discovery of benzene in 1825 are discussed. Using modern techniques of instrumental analysis, the author retraces the isolation and analysis of benzene, and shows that the starting material used by Faraday must have been a very complex mixture of hydrocarbons, which would make severe demands even on present-day preparative analytical techniques, since it contains more than 300 components at concentrations greater than 100 ppm. The magnitude of the changes in analytical techniques can be seen from the fact that it is no longer necessary to isolate individual compounds, and that a great deal of information can be obtained with a much smaller quantity of material and in a much shorter time. Nevertheless, Faraday's persistence, experimental skill, and accuracy of measurement remain an example to the analyst of today.     

Evaluation of syringe handling techniques for injections into vaporizing GC injectors

Unequal elution of sample components of different volatility out of the syringe needle is one of the major causes for discrimination occuring during the injection, i.e. the phenomena which results in peak areas for the high boiling compounds which are too small compared with the volatiles. This problem, associated with all vaporizing injectors that are used with syringes, can be minimized by careful choice of the needle handling technique. Various methods are compared experimentally. The “solvent flush” method is discussed in detail and demonstrated to be ineffective for reducing losses in the syringe needle. The “hot needle” technique, where the empty needle is preheated in the injector before pushing the plunger, was found to be superior or equal to an improved “solvent flush” method (which included preheating the needle and omitting the air plug between sample and flushing solvent. Generally it was found that the discrimination due to the syringe needle was reduced for larger sample volumes, although no further changes were noticed when these exceeded 2.5 to 3μl.     

„Ytterbiumdisulfid”︁: Eine Korrektur

?Ytterbiumdisulfide”?: A Correction The still open questions concerning preparation and crystal structure of ?Ytterbiumdisulfide”? could be answered now using new experimental results. The formerly investigated single crystals were not Yb^IIS₂ but BaS₂.     

Selective Alkaline Protease Catalyzed Hydrolysis of Peptide Esters

Procedures for preparing C-terminal free peptides from hydrolysis of its corresponding methyl or benzyl esters catalyzed by alkaline protease has been developed. N-protected peptides having side-chain ester protecting groups or successive hydrophobic amino acid residues in its sequence are hydrolyzed selectively at C-terminal only and leave other bonds (β and γ- ester or peptide bonds) intact. Compounds which cause a side reaction in base mediated saponification could be hydrolyzed safely by this procedure. Products of this hydrolysis are useful intermediates for fragments coupling in the solid phase peptide synthesis.     

Synthesis of new 1<Emphasis Type="Italic">H</Emphasis>-pyridazine derivatives <Emphasis Type="Italic">peri</Emphasis>-annelated with acenaphthene and acenaphthylene

The reaction of 6-acetyl-5-hydroxyacenaphthene with methylhydrazine afforded 1,3-dimethyl-1H-6,7-dihydroacenaphtho[5,6-de]pyridazine. Its dehydrogenation with chloranil gave 1,3-dimethyl-1H-acenaphtho[5,6-de]pyridazine, which is a heteroaromatic compound with an essentially new topology of the ρsystem. The reaction of 3-methyl-1H-6,7-dihydroacenaphtho[5,6-de]pyridazine with 3,5-di-tert-butyl-1,2-benzoquinone yielded a dimer containing the acenaphthene and acenaphthylene moieties of peri-annelated 1H-1,2-diazines connected in positions 1′ and 9.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 777–780, March, 2005.     

Efficient synthesis of monodisperse,highly crosslinked,and “living” functional polymer microspheres by the ambient temperature iniferter‐induced “living” radical precipitation polymerization

The facile and efficient one‐pot synthesis of monodisperse, highly crosslinked, and “living” functional copolymer microspheres by the ambient temperature iniferter‐induced “living” radical precipitation polymerization (ILRPP) is described for the first time. The simple introduction of iniferter‐induced “living” radical polymerization (ILRP) mechanism into precipitation polymerization system, together with the use of ethanol solvent, allows the direct generation of such uniform functional copolymer microspheres. The polymerization parameters (including monomer loading, iniferter concentration, molar ratio of crosslinker to monovinyl comonomer, and polymerization time and scale) showed much influence on the morphologies of the resulting copolymer microspheres, thus permitting the convenient tailoring of the particle sizes by easily tuning the reaction conditions. In particular, monodisperse poly(4‐vinylpyridine‐co‐ethylene glycol dimethacrylate) microspheres were prepared by the ambient temperature ILRPP even at a high monomer loading of 18 vol %. The general applicability of the ambient temperature ILRPP was confirmed by the preparation of uniform copolymer microspheres with incorporated glycidyl methacrylate. Moreover, the “livingness” of the resulting polymer microspheres was verified by their direct grafting of hydrophilic polymer brushes via surface‐initiated ILRP. Furthermore, a “grafting from” particle growth mechanism was proposed for ILRPP, which is considerably different from the “grafting to” particle growth mechanism in the traditional precipitation polymerization. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Hopping conduction in “pure” polypropylene

A recently developed theory of steady-state conduction in high-density polyethylene is applied to “pure” polypropylene (PP) in the temperature range 50–93°C. Morphological changes occur in PP, including a disordered-amorphous to monoclinic-amorphous transition between 50 and 80°C, where, with increasing temperature T, free volume increases, and decreases with decreasing amorphous fraction. The latter competing processes lead to large increases in hopping site separation, λ, in the transition region, followed either by saturation or a maximum in λ vs. T. We speculate that segmental and/or main chain molecular motions lower apparent activation energies, are “pinned“ by applied field, and impeded by dangling bonds in regions surrounding the surfaces of crystallites. Our analysis is semi-quantitative only, because the latter mechanisms have not been adequately quantified, and the relative contributions of each are unknown. Measurements were carried out on heated and cooled disordered-amorphous, and 106°C, 17-h annealed, 43% crystalline samples. Hopping distances, obtained from measured current vs. applied field characteristics, ranged from 1.2 to 5.2 nm. Apparent activation energies up to 1.80 eV were obtained from In (I/T) vs. (1/T) plots. Remarkable plateaus in the temperature range of the transition were observed in these plots, implying some carrier conduction with near zero activation energy. Possible explanations for the latter, and the electronic nature of the carriers are given. X-ray and density flotation measurements enabled crystallinity determinations. © 1994 John Wiley & Sons, Inc.     

Facile synthesis of polyester dendrimer via combining thio‐bromo “Click” chemistry and ATNRC

This article reports on developing an efficient synthesis approach to aliphatic polyester dendrimer, poly(thioglycerol‐2‐propionate) (PTP), by combination of thio‐bromo “Click” chemistry with atom transfer nitroxide radical coupling (ATNRC). Through the one‐pot two‐step method, linear polystyrene with hydroxyl end groups (l‐PS‐2OH) was obtained by first atom transfer radical polymerization of styrene and following termination using 4‐(2,3‐dihydroxypropoxy)‐TEMPO (DHP‐TEMPO) to capture the PS macroradicals via ATNRC method. Using l‐PS‐2OH as support, the dendritic repeating units divergently were grown from the hydroxyl end groups via esterification and thio‐bromo “Click” reaction two‐step process. In every generation, the resulting intermediates l‐PS‐d‐PTP (G1‐G4) can be easily isolated from the excessive unreacted monomers by simple precipitation in ethanol without help of time, labor and solvent consuming column chromatographic purification. At last, cleavage of the alkoxyamine group between the PS support and dendrimer at elevated temperature (125 °C) provided the targeted polyester dendrimer PTP up to the fourth generation. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1762–1768     

Adsorption of <Emphasis Type="Italic">n</Emphasis>-Butanol from Aqueous Solutions on an Sn-Ga Electrode in the Absence of a Metal-Water Chemisorption Interaction

Data on the dependence of the differential capacitance on potential at the Sn-Ga/H₂O interface in 0.05 M solutions of Na₂SO₄ with various additives of n-butanol are obtained by a bridge method at a frequency of 420 Hz and a temperature of 32°C. In the region of potentials studied, the chemisorption interaction (Sn-Ga)-H₂O is completely absent. The adsorption parameters of n-butanol are obtained by a method of a regression analysis of these data. The data obtained are compared with similar data on various hydrophobic electrodes. Shown is that, on the Sn-Ga and Pb-Ga electrodes, whose “electronic” capacitance is similar, the free energies of adsorption of n-butanol are also similar but differ from the adsorption energy on electrodes of Hg, Bi-Ga, and Tl-Ga. The results that are obtained on an Sn-Ga electrode nicely fit a general correlation dependence between the reciprocal value of the electronic capacitance of various electrodes in the absence of a metal-water chemisorption interaction, (C _m ⁻¹ ), and the free energies of adsorption of molecules of n-butanol on these, ΔG _A ⁰ . The dependence of the free energies of adsorption of molecules of n-butanol in the absence of a metal-water chemisorption interaction on the magnitude of the electronic capacitance of the metal confirms the assumption that we had put forth previously that it is necessary to introduce corrections to criteria of hydrophilicity of metals based on a comparison of quantities ΔG _A ⁰ and potentials of cathodic peak of adsorption-desorption E _des, which are expressed in a rational scale. With the obtained correlation relationships taken into account, criteria of hydrophilicity are suggested, which take into account these correlation relationships.__________Translated from Elektrokhimiya, Vol. 41, No. 7, 2005, pp. 884–892.Original Russian Text Copyright © 2005 by Emets, Damaskin.     

On the applicability of the “abt” concept

Kaiser's “abt” concept rests on the experimental establishment of a linear relation between band width at half height, b_0.5, and capacity ratio, k, according to His column specification quantity, h_real, is dependent on the square of the slope a, obtained from a linear regression analysis based on this relation. It is shown in the present paper that an improvement of the experimental conditions leading to a lower extra-column contribution to band broadening, b, introduces a tendency towards a negative curvature in the plot at low k values. The mean slope increases, and an uncritical linear regression would yield an h_real-value which is higher than before and which would be in the opposite direction to the requirements of a reliable column specification. Generally the linear regression analysis has to be moved to higher k regions in cases of curvature, especially as it is also shown that h_real is an estimation of the traditional HETP value, H∞, that would be obtained when k approaches infinity. This theoretically expected relation is a strong motivation for the use of h_real as a column specification, since the b_0.5-value associated with H∞ is expected to be practically independent of b.     

A “quasi‐flexible” automatic docking processing for studying stereoselective recognition mechanisms. Part I. Protocol validation

The main purpose of this work is the development and validation of a general scheme based on a systematic and automatic “quasi‐flexible” docking approach for studying stereoselective recognition mechanisms. To achieve our goals we explore the conformational and configurational space for small‐ or medium‐size flexible molecules in a systematic way, seeking a method that is both reasonably accurate and relatively fast from the computational point of view. In particular, we have developed a general computational protocol for the global molecular interaction evaluation (“Glob‐MolInE”) to efficiently explore the orientational and conformational space of flexible selectors and selectands used in modern chiral high‐performance liquid chromatography (HPLC); the enantioselective binding of the selector (S)‐N‐(3,5‐dinitrobenzoyl)‐leucine‐ n‐propylamide (S)‐ 1 towards the selectand N‐(2‐naphthyl)‐alanine methyl ester 2 has been studied; the global minimum obtained for the homochiral associate [S( 1 )/S( 2 )] (Pop. >99%) is very close (RMS≃0.20) to the crystallographically determined structure. © 2000 John Wiley & Sons, Inc. J Comput Chem 21: 515–530, 2000     

On the statistical independence of various column contributions to band broadening. Part 3: Independent treatment of longitudinal diffusion in the plate model

It is shown theorectically that the classical formula for calculating the theoretical plate number from squared first central moment, t , and second central moment, σ², according to n _theor = t /σ² is valid only when the capacity ratio, k approaches infinity. The general relation between the classical experimental HETP value, H = L/nm _theor, and the underlying true theoretical plate height, ΔL, is found to be when (σ′)² is the total column contribution to band broadening, L is the column length, D _m is the average diffusion coefficient of the sample component in the mobile phase, D _s is its value in the stationary phase, and u is the average linear velocity of the mobile phase. The mobile phase displacement, as well as the mass exchange process, is assumed to be continuous, but the application of the plate concept conditions leads to a mass balance equation that can be interpreted as belonging to a modified discontinuous plate model. The contributions 2D _m/u and k 2 D _s/u from longitudinal sample diffusion in the mobile and stationary phases, respectively, are consistent with the assumption that the processes are statistically independent, although the common solution technique of the differential equations does not take full account of this independence.     

Synthesis and characterization of star graft copolymers with asymmetric mixed “V‐shaped” side chains via “click” chemistry on a hyperbranched polyglycerol core

The star graft copolymers composed of hyperbranched polyglycerol (HPG) as core and well defined asymmetric mixed “V‐shaped” identical polystyrene (PS) and poly(tert‐butyl acrylate) as side chains were synthesized via the “click” chemistry. The V‐shaped side chain bearing a “clickable” alkyne group at the conjunction point of two blocks was first prepared through the combination of anionic polymerization of styrene (St) and atom transfer radical polymerization of tert‐butyl acrylate (tBA) monomer, and then “click” chemistry was conducted between the alkyne groups on the side chains and azide groups on HPG core. The obtained star graft copolymers and intermediates were characterized by gel permeation chromatography (GPC), GPC equipped with a multiangle laser‐light scattering detector (GPC‐MALLS), nuclear magnetic resonance spectroscopy and fourier transform infrared. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1308–1316, 2009     

Synthesis and characterization of surface‐initiated polymer brushes on silicon substrates by reversible addition fragmentation chain transfer polymerization

Polymer brushes were prepared by using the reversible addition fragmentation chain transfer (RAFT) technique. The silicon substrates (Si (111) surface) were modified with ethyl xanthate groups which were introduced by the treatment of Si (111) surface with sodium ethyl xanthate. The polymer brushes were then prepared under RAFT conditions from the Si (111) wafer. Its “living” characteristics were determined by a series of characterizations including gel permeation chromatography (GPC), ellipsometry, and contact angle measurements. The results showed a well‐defined graft layer consisting of polymer brushes with low‐polydispersity could be prepared directly on Si (111)‐X surface (where X represents an ethyl xanthate groups). The structure of the polymer brushes was characterized and confirmed with the surface sensitive techniques such as X‐ray photoelectron spectroscopy (XPS) and scanning probe microscopy (SPM). Copyright © 2007 John Wiley & Sons, Ltd.