Is Chromatography a Science, a Process, a Method, or a Scientific Discipline?

In the controversy over an article entitled Chromatography as a Scientific Discipline by V.G. Berezkin, it was pointed out that the subdivision of chromatographic processes into sorption–sieve chromatography and field nonsorption chromatography is inadmissible. It was demonstrated that all chromatographic processes, including flow fractionation in a transverse force field, are in principle two-phase (or polyphase) processes. It was illustrated that a longitudinal field in a flow cannot introduce a chromatographic component into the system. An additional definition of chromatography as a phenomenon was proposed on the basis of key points revealed by Professor Berezkin.     

When is a metallopolymer not a metallopolymer? When it is a metallomacrocycle

We report reactions of cobalt(II) acetate with a series of ditopic bis(tpy) ligands (tpy = 2,2':6',2'-terpyridine) containing flexible polyethyleneoxy spacers (tpy-4'-O{(CH(2))(2)O}(n)-4'-tpy, n = 2, 3, 4 or 6 ligands 1-4, respectively) which result in the formation of complicated mixtures of species, presumed to be both open chain and cyclic species. Well resolved paramagnetically shifted (1)H NMR spectra are a powerful tool for the analysis of these solution systems. Upon equilibration, [n + n] metallomacrocycles are isolated as the dominant (thermodynamic) species in some cases, and the single crystal X-ray structures of [Co(2)(3)(2)][PF(6)](4)·6MeCN and [Co(2)(4)(2)][PF(6)](5)·2MeCN (a mixed cobalt(ii)/cobalt(iii) species) are presented. Oxidation of the equilibrated cobalt(II) mixtures to kinetically inert cobalt(III) species provides additional evidence for the formation of metallomacrocycles as the thermodynamic products. Single crystal structural data for [Co(3)(2)(3)][PF(6)](9)·2MeCN·3.5H(2)O, [Co(2)(3)(2)][PF(6)](6)·10MeCN and [Co(2)(4)(2)][PF(6)](6)·6MeCN confirm the assembly of [2 + 2] and [3 + 3] metallomacrocycles. PGSE NMR spectroscopy has been used to determine the hydrodynamic radii of the solution species.     

Simulation of a flow of a “Sedate” reaction mass in a screw reactor with a thin wall layer

A transition to a flow virtually non-gradient in a screw reactors of heavy sedate liquid with thin wall layer is considered. The graphs of the differential response functions of the known models based on the ideal gas law for structures of flows (ideal mixture, ideal displacement, laminar and turbulent flows) in comparison with the response function of the sedate reaction mass were presented. The flow structure corresponds to the regime of the ideal displacement in the screw reactor at a treatment of the sedate reaction mass when air, water or other thin liquid are fed as lubricant in the wall layer.     

When does a hydrogen bond become a van der Waals interaction? a topological answer

The hydrogen bond (H-bond) is among the most important noncovalent interaction (NCI) for bioorganic compounds. However, no “energy border” has yet been identified to distinguish it from van der Waals (vdW) interaction. Thus, classifying NCIs and interpreting their physical and chemical importance remain open to great subjectivity. In this work, the “energy border” between vdW and H-bonding interactions was identified using a dimer of water, as well as for a series of classical and nonclassical H-bonding systems. Through means of the quantum theory of atoms in molecules and in particular the source function, it was possible to clearly identify the transition from H-bonding to vdW bonding via analysis of the electronic structure. This “energy border” was identified both on elongating the interatomic interaction and by varying the contact angle. Hence, this study also redefines the “critic angle” previously proposed by Galvão et al. (J. Phys. Chem. A 2013, 117, 12668). Consequently, such “energy border” through an analysis of atomic basins volume variation was possible to identify the end of long-range interactions. © 2019 Wiley Periodicals, Inc.     

Reference materials – a view from a small country

ISO/IEC 17025 has an increased emphasis on traceability and estimation of uncertainty of measurement compared with ISO Guide 25. Demonstration of traceability is a new concept in analytical chemistry and depends on access to relevant reference materials or use of reference methods. Until now most reference materials used in New Zealand have been imported, because they offered international comparability. New Zealand is currently starting to develop the required infrastructure so that it will be able to produce unique reference materials that will contribute to the total international effort in improving the reliability of analytical chemistry. Received: 12 October 2000 / Revised: 18 January 2001 / Accepted: 23 January 2001     

Is a Bent Crystal Still a Single Crystal?

The mention of the word “crystal” invokes images of minerals, gems, and rocks, all of which are inevitably solid, hard, and durable entities with well‐defined smooth faces and straight edges. With the discovery in the first half of the 20th century that many molecular crystals are soft and can be deformed in a similar way as rubber or plastic, this perception is changing, and both the concept and formal definition of what a crystal is may require reinterpretation. The seemingly naïve question posed in the title of this Minireview does not have a simple answer. Here, we discuss how the effects of the elastic and plastic deformation of molecular crystals on the diffraction signature give primary evidence of their degree of crystallinity. In most cases, the definition of a crystal holds for both elastically and plastically deformed crystals and, unless there is significant or complete physical separation of the crystal during the deformation, they can safely be considered (deformed) single crystals with a high concentration of defects.     

Comparative studies on a mesophilic and a thermophilic α-amylase

A comparative study was performed on thermal stability of mesophilic and thermophilic α-amylases, and the effects of various denaturing agents, organic solvents, and stabilizers were investigated. As expected, the thermophilic enzyme showed higher resistance toward denaturation in water as its natural medium, but such a difference could not be detected in nonaqueous environments. Furthermore, stability of these molecules was improved by including various stabilizing agents. Of the compounds tested, sorbitol provided the highest degree of protection, which was found to be owing to its effect on increasing T _m and its ability in totally preventing deamidation of amino acid residues in the protein molecules.     

Unusual shift of a nitro group in a phenylhydrazo-β-diketone

A novel para to meta shift of a nitro group at the phenyl ring of 3-(2-hydroxy-4-nitrophenylhydrazo)pentane-2,4-dione (H(2)L(1), 1), with formation of the new 3-(2-hydroxy-3,5-dinitrophenylhydrazo)pentane-2,4-dione (H(2)L(2), 2), occurs upon nitration of 1 with an equimolar amount of NaNO(2), under basic conditions. 2 acts as a polydentate ligand for the synthesis of the polymeric potassium [K(μ(5)-HL(2))](n) (3) and monomeric nickel(II) [Ni(H(2)O)(3)(L(2))]·H(2)O (4) compounds. They have been fully characterized, including single crystal X-ray analysis, and the complexes feature metal-organic (in 3) or supramolecular (in 4) 3D networks. The topological analysis of 3 reveals a uninodal 5-connected underlying net with the point symbol of (4(6).6(4)) and a very rare 5/4/t5 topology, which had not yet been observed in coordination polymers.     

Synthesis of a novel cyclodextrin dimer linked by a macrocyclic polyamine

The first example of cyclodextrin dimer appending a macrocyclic polyamine spacer on the primary faces was synthesized via two approaches: 1,a direct reaction of l,7-bis(2'-aminoethyl)-4,10-dimethyl-l,4,7,10-tetraazacyclododecane (1) with an excess of 6-deoxy-6-O-tosyl-β-cyclodextrin; 2,a condensation of 1 with two equivalents of 6-deoxy-6-formyl-β-cyclodextrin,which was followed by a reduction with NaBH4.     

Solution structure of a DNA duplex containing a guanine-difluorotoluene pair: a wobble pair without hydrogen bonding?

The incorporation of synthetic nucleoside analogues into DNA duplexes provides a unique opportunity to probe both structure and function of nucleic acids. We used 1H and 19F NMR and molecular dynamics calculations to determine the solution structures of two similar DNA decamer duplexes, one containing a central G-T mismatched or "wobble" base pair, and one in which the thymine in this base pair is replaced by difluorotoluene (a thymine isostere) creating a G-F pair. Here, we show that the non-hydrogen-bonding G-F pair stacks relatively well into the helix and that the distortions caused by each non-Watson-Crick G-T or G-F base pair are quite localized to a three base pair site around the mismatch. A detailed structural analysis reveals that the absence of hydrogen bonding introduces more dynamic motion into the G-F pair relative to G-T and permits the G-F pair to exhibit stacking and conformational features characteristic of both a Watson-Crick base pair (on the guanine containing strand) and a wobble base pair (on the strand containing the difluorotoluene). We used these results to posit a rationale for recognition and repair of mismatch sites in DNA.     

Making Ecology a Priority

China‘s outstanding economic achievements in recent years have been partly based on an excessive consumption of its energy resources.     

Unusual Formation of a β-linked Disaccharide in a Nis Glycosylation

Abstract

The N-halosuccinimide glycosylation is a highly selective reaction that leads to trans-configured 1-alkoxy-2-halo-glycosides (halo = bromo, iodo).²³ As an exception to the generally observed exclusive formation of α-linked glycosides in such reactions,² we obtained a 3 / 1 mixture of α- and β-disaccharide 6 and 7, when we treated the silylated glycal 4 with NIS (N-iodosuccinimide) and the glycoside 5.⁴ The similarly protected arabino glycal 9, on the other hand, gave exclusively the expected α-linked saccharide 11, when treated with NIS and the alcohol component 10.⁵ Silylated glycals 4 and 9 were obtained from L-digitoxal 1 ⁶ and L-rhamnal 8 ⁷ by treatment with tert-butyldiphenylchlorosilane⁸ and tert-butyldimethylchlorosilane,⁹ respectively. In both cases the 3-O-silylated derivatives formed in high yields. Only in case of the ribo-configuration minor amounts of a 4-O-silylated product 3 were identified.     

Electrospray ionization suppression,a physical or a chemical phenomenon?

Mass spectrometry is a powerful qualitative and quantitative analytical technique that has been introduced in many bioanalytical and research laboratories in the last 10 years. The combination of HPLC with tandem MS yields a particularly powerful tool and it is now the method of choice for the analysis drugs, metabolites, biomarkers and proteins. However, HPLC-MS methods are not completely without problems that can compromise the quality of the results. An important phenomenon that can affect the quantitative performance of a mass detector is ion suppression. In this study, we measured the influence of the observed current (I) vs signal intensity and the variation of the observed current (I) when analyzing biological samples. Our experiment suggests that, despite the fact that it is possible for other chemicals to compete for protons in the droplets, the increase in the observed current (I) during the signal suppression is important and indicates that the conductivity of the liquid increases significantly. The salts and the charged species influence the conductivity and the surface tension of the droplets and modify the equilibrium between the two main forces involved during the electrospray process, resulting in an erratic spray behavior.     

Hydroacridines XXI [1]. 13C NMR Spectroscopic Investigation of the Stereoselectivities of Quaternizations of N-Alkyl Derivatives of (4aα,8aβ,9aβ,10aα)- and (4aα,8aα,9aβ,10aα)-Tetradecahydroacridine

Summary.  The stereoselectivities of the quaternization reactions of (4aα,8aβ,9aβ,10aα)- and (4aα,8aα,9aβ,10aα)-tetradecahydro-10-methylacridine with methyl- and ethyl iodide as well as those of (4aα,8aβ,9aβ,10aα)- and (4aα,8aα,9aβ,10aα)-10-ethyl-tetradecahydroacridine with methyl iodide were investigated using ¹³C NMR spectroscopy including ¹³C-labelling where appropriate. The methylations of both N-methyl amines occur by predominant (60% and 75%, respectively) equatorial approach, their ethylations occur sterospecifically by equatorial approach, and the methylations of the N-ethyl amines occur by highly stereoselective (> 90%) axial approach of the quaternizing reagent. Received October 27, 1999. Accepted November 22, 1999     

Enclosure of a Keggin-type heteropolyoxometalate into a tubular π-space via hydrogen bonds with a nonplanar Mo(V)-porphyrin complex forming a supramolecular assembly

A 2:1 supramolecular assembly composed of a non-planar Mo(V)-porphyrin, [Mo(DPP)(O)(H(2)O)](+) (1) (DPP(2+); dodecaphenylporphyrin), and a Keggin-type heteropolyoxometalate (POM), α-[(n-butyl)(4)N](2)[SW(12)O(40)] (2), was formed via hydrogen bonds. The crystal structure was determined by X-ray crystallography to clarify that the POM was enclosed into a π-space of a supramolecular porphyrin nanotube by virtue of a hydrogen-bond network. In contrast to the formation of the 2:1 assembly ([{Mo(DPP)(O)(H(2)O)}(2)(SW(12)O(40))] (3)) between 1 and [SW(12)O(40)](2-) in the crystal, it was revealed that those two components form a 1:1 assembly in solution, in light of the results of MALDI-TOF-MS measurements in PhCN. Variable-temperature UV-vis spectroscopic titration allowed us to determine the thermodynamic parameters for the formation of the 1:1 supramolecular assembly in solution, the heat of formation (ΔH) and the entropy change (ΔS). These results provide the first thermodynamic data set to elucidate the formation process of supramolecuar structures emerged by hydrogen bonding between metalloporphyrin complexes and POMs, indicating that the formation of the assembly is an entropy-controlled process rather than an enthalpy-controlled one. Comparisons of the thermodynamic parameters with those of a planar Mo(V)-porphyrin complex also highlighted high Lewis acidity of the Mo(V) centre in the distorted porphyrin.     

Cyclodextrin as a Template for Molecular Assembly: Formation of Heterodimers Between a Polyamino- and a Polysulfonato-β-Cyclodextrin

A poly(hydroxyethylamino)- and a poly(sulfonatophenyloxy)--cyclodextrin derivative, bearing opposite ionic charges, have been shown by potentiometric titration to form stable pH-dependent heterodimers with each other in water. The formation constants of these dimers show that a very stable assembly is formed between the fully deprotonated sulfonato derivative and the fully protonated amino derivative (log K_a = 8.5), which constitutes the assembly of multiple extended atomic groupings on cyclodextrin as template.     

The Reduction of a Natural Diterpene Containing a, B-Unsaturated Keto Group

Hedychenone (1), a diterpene containing a, B-unsaturated keto group, was reduced by aluminum-mercury alloy, and a dimerized product (2) was obtained as the major product. The coupling occurred at B position of the keto group.