‘Apples’ and ‘oranges’: comparing the structural aspects of biomineral- and ice-interaction proteins

The title of this review describes structural comparisons of protein classes whose task is to identify and interact with biological solids (minerals and ice). To date, the following trends have been noted: (1) biomineral-interaction proteins typically adopt unfolded, open conformations, and, where mineral binding motifs have been identified, these sequences exhibit structural trends towards extended, random coil, or other unstable secondary structures; (2) ice-interaction proteins typically adopt folded structures, featuring stable secondary structure preferences (α-helix, β-sheet, β-helix, etc.) and stable, planar ice binding motifs that exploit hydrophobicity and van der Waals’ interactions for ice binding.     

Generic division of ‘quantity’ and related terms

In the slow evolution of the International vocabulary of metrology (VIM), the first concept of ‘quantity’ has now been divided generically into ‘ordinal quantity’ and a coordinate primitive without definition and term. An analysis of the concepts by their characteristics is made, and the nature of inheritance is discussed in response to a recent communication in this journal. A completion of the initiated generic division of ‘quantity’ is suggested, and a neoterm for the sister of ‘ordinal quantity’ is offered on the basis of two proposals.     

Synthesis and complexation of a ‘mixed’-pyridine-naphthalene homooxacalixarene

A deep-cavity ‘mixed’ octahomotetraoxacalix[2]naphthalene[2]pyridine macrocycle has been synthesised and its single-crystal X-ray structure has been determined. Molecular modeling studies suggested that this macrocycle could be an effective host for guest aromatic diol(s) similar to Wang's methylazacalixpyridines. Binding constants were determined using ¹H NMR chemical shifts changes and comparisons were made between the diols which were tested.     

Synthesis and Crystal Structure of N—（1‘’‘’—Phenyl—2‘’‘’—hydroxyethyl）—2,3—naphthylenedicarboximide

IntroductionThe design and the synthesis of new chiral ox-azoline[1,2 ] and C2 symmetric bis( oxazoline) ligandsand the application of their metal complexes inasymmetric catalytic reactions have inspired manyscientists to great exertions in recent years[3— 8] .Our interest has been focussed on the studies ofenantioselective transition metal catalysis ofhetero-cyclic ligands[9— 11] . In the synthesis of our new de-signed ligands,what is crucial is to select a rigidcyclic backbone. Bis( oxazo…     

The Emergence and Properties of Selectively Fluorinated ‘Janus’ Cyclohexanes

This account describes the evolution of a research programme that started by linking fluoromethylene (−CHF−) groups along aliphatic chains and then progressing to alicyclic rings with contiguous fluorine atoms. Different stereoisomers of aliphatic chains tend to adopt low polarity conformations. In order to force polar conformations, the programme began to address ring systems and in particular cyclohexanes, to restrain conformational freedom and co-aligned C−F bonds. The flagship molecule, all-cis-1,2,3,4,5,6-hexafluorocyclohexane 7 , emerged to be the most polar aliphatic compound recorded. The polarity arises because there are three co-aligned triaxial C−F bonds and the six fluorines occupy one face of the ring. Conversely the electropositive hydrogens occupy the other face. These have been termed Janus face cyclohexanes after the Roman god with two faces. The review outlines progress by our group and others in preparing derivatives of the parent cyclohexane 7 , in order to explore properties and potential applications of these Janus cyclohexanes.     

‘Pincer’ pyridyl- and bipyridyl-N-heterocyclic carbene analogues of the Grubbs’ metathesis catalyst

The ‘pincer’ pyridine-dicarbene and bipyridyl-carbene ruthenium benzylidene complexes, Ru(C–N–C)Cl₂(CHPh) and Ru(C–N–N)Cl₂(CHPh), (C–N–C) = 2,6-bis(DiPP-imidazol-2-ylidene)pyridine, (C–N–N) = (DiPP-imidazol-2-ylidene)bipyridine, have been prepared and characterised by spectroscopic and diffraction methods. They exhibit moderate metathesis activity. Non-symmetrical linear tridentate ether-functionalised N-heterocyclic carbene pro-ligands are also described.     

The meaning of ‘concentration’

Terminology within a small laboratory community can be informal without danger of misunderstanding, but communication with a wider audience and not least in publications, needs unequivocal terms for defined concepts. As an example, the many meanings of “concentration” are explored to present a systematic nomenclature, including a concept diagram.

Syntheses and Crystal Structures of 4,4‘—Diformyl—diphenoxyethane and 4,4’,4‘’—Triformyl—triphenoxytriethylamine

Two title compounds, 4,4'-diformyl-diphenoxyethane (compound 1, C16H14O4)and 4,4',4'-triformyl-triphenoxytriethylamine (compound 2, C27H27NO6), were synthesized by condensation of 4-hydroxybenzaldehyde with 1,2-dichloroethane and tris2-chloroethylamine, respectively in dimethyl formamide in the presence of anhydrous potassium carbonate. The crystal data are: monoclinic, P21/c, a = 7.571(2), b = 12.608(3), c = 7.357(2) ', = 105.823(6)o, V = 675.7(2)'3, Mr = 270.3, Z = 2, Dc = 1.328 g/cm3, F(000) = 284, (MoK = 0.096 mm-1, R = 0.0537 and wR = 0.2189 for compound 1; and monoclinic, P21/n, a = 11.7162(6), b = 9.0042(6), c = 22.908(2) ', = 99.505(1)°, V = 2383.5(3) '3, Mr = 461.50, Z = 4, Dc = 1.286 g/cm3, F(000)= 976, (MoK = 0.091 mm-1, R = 0.0464 and wR = 0.1462 for compound 2. The molecule of compound 1 dialdehyde is located at the crystallographic inversion center nearby the midpoint of C8-C8A single bond. The three chains in the molecule of compound 2 trialdehyde are of non-crystallographic pseudo-C3 symmetry, and each of them is quite planar.     

On the boundary between laboratory ‘givens’ and laboratory ‘tangibles’

From the 4-part Procedure/Observations/Data/Analysis structure of a laboratory report (generalized from Italian, Chinese and US sources), we distill a fifth flavor, the givens, whose flip side is the freedoms or tangibles of an experiment. (Stated in terms of computer science, we are trying to find inputs and outputs, but these turn out to be surprisingly vague in chemistry.) Then, in the service of a white-boxing ethos (which sounds less severe than ‘anti black-boxing’), we establish a movable boundary between givens and tangibles, with implications for ‘ontological attitudes’ and for the future of chemistry. Next, in revisiting a 2002 exchange between Schummer and Laszlo, which might be paraphrased as the chemist-as-philosopher versus chemist-as-artisan, we apply a second kind of sliding scale which seems to harmonize the discussion. Finally, on a possibly quixotic note, we look briefly at a third kind of sliding scale, now aimed squarely at ontology itself. For illustrative purposes, we adopt an atomocentric viewpoint (as distinct from atomistic), and assign it the provisional name ‘Fuzzy CH₄ Ontology’.     

Thermal investigation of ‘molten starch’

Detailed thermal analysis studies have shown that a ‘molten starch’ phase is obtained during controlled heating of starch. Before the ‘molten’ stage, depolymerisation of starch produces lower molecular weight compounds like dextrins, oligo, di- and monosaccharides, as well as other types of compounds. These compounds should have ideal properties for plasticizing starches because of the similarities of the molecules, helping lower phase changes in collaboration with molecular weight decrease. Interestingly, it was found previously that these materials only act as adhesives in a narrow temperature range around 523 K (250 °C) (Shuttleworth et al. J Mater Chem 19(45):8589–8593, 2009). Materials were investigated using thermal and mechanical analyses of single lap joints.     

Comparison of Experimental Methods and Theoretical Calculations on Crystal Energies of ‘Isoenergetic’ Polymorphs of Cimetidine

The thermodynamic energy relationship between two crystal modifications of cimetidine was investigated and compared with differences in their processing properties with respect to transformation from one modification to the other.The crystal energies of the two modifications A and D were found to be almost identical and therefore the polymorphs are regarded as virtually isoenergetic crystals. This statement is based on DSC measurements of the melting points and of the enthalpies of fusion for the two crystal forms, which enable the calculation of the Gibbs free energy functions. Furthermore, the statement is supported by measurements of the enthalpies of solution in two different solvents. Both DSC and solution experiments reveal a slightly higher stability of the D modification with respect to the A form. In addition, tribomechanical treatment also indicates modification D to be the more stable one, as well as the higher density of the D form. No transformation during DSC at low heating rate was found which could be used in a stability consideration.As the explicit crystal structures of the two modifications are resolved, it was possible to calculate crystal energies theoretically as well. The theoretical results showed a remarkable difference in the crystal energies at zero degree Kelvin. Furthermore, they were just contradicting experimental findings by stating A being more stable than D. Possible reasons for this discrepancy and the feasibility of today's calculation methods with respect to prediction of stability properties are discussed.This revised version was published online in November 2005 with corrections to the Cover Date.     

HPLC-spectrophotometric detection of trace heavy metals via ‘cascade’ separation and concentration

A cascade pre-concentration and separation system involving continuous solid-phase extraction and one-drop solvent concentration was developed to enable high-performance liquid chromatography (HPLC) determination of trace levels of Ni(II), Co(II), Cu(II), Se(IV) and Cr(VI) ions in aqueous solution via complexation with sodium diethyldithiocarbamate. The metal complexes were almost completely adsorbed on the solid phase (octadecylsilyl packed column). Ethyl acetate (eluent) containing the metal complexes was then placed in a centrifuge tube, to which a microvolume of dimethyl sulfoxide (DMSO) was added. Successful pre-concentration of the metal complexes into the DMSO phase was accomplished by removing the ethyl acetate using a compact evaporator in a water bath (40°C); 1000-fold concentration was achieved within 45 min. A portion of the residual DMSO phase was then subjected to HPLC analysis. The proposed method has high reproducibility and high sensitivity with detection limits (3σ) for Ni(II), Co(II), Cu(II), Se(IV) and Cr(VI) ions of 0.08, 0.11, 0.12, 0.44 and 0.20 µg/L, respectively. Relative standard deviations (RSDs) (n = 5) at Ni(II) 5.87 µg/L, Co(II) 5.89 µg/L, Cu(II) 6.35 µg/L, Se(IV) 7.90 µg/L and Cr(VI) 5.20 µg/L (1.0 × 10^?7 mol/L each) were 4.0%, 4.6%, 4.6%, 7.2% and 3.4%, respectively.     

Molecular ‘OR’ and ‘AND’ logic gates integrated in a single molecule

Based on the N electrodes elastic scattering quantum chemistry (NESQC) technique, an intramolecular circuit simulator is presented for the design of electronic logic functions integrated inside a single molecule interconnected to the N electrodes. Using molecular rectifier groups, a molecule-OR and a molecule-AND are designed, their current-voltage characteristics calculated and their logic response presented. Both the OR and AND molecules have approximatively the targeted function. The running current of the OR gate, 10 fA, is quite low and the AND gate works only in an output voltage mode. This forbids the design of larger logic functions inside a single molecule with molecular rectifiers.     

Solid-state crystallization process and mechanism of B-Al-ZSM-5 zeolite

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Action mechanism of antioxidation and anticorrosion and molecular design for perfluoropolyether fluid additives (Ⅰ)——Action mechanism of additive and property of donating-accepting electron

The combination energy and chemical adsorption energy of N-substituted perfluoropoly-alkyletherphenylamide (PFPEA) additive to perfluoropolyalkylether oxygen radical (RfO.) and to Fe atom have been calculated by quantum chemical methods. Structural characteristics, action mechanism, property of donating-accepting electron and substituent effect for antioxidant and anticorrosive additive are investigated. It is found that HOMO of the additives is a π-molecular orbital with lone pair electron of heteroatom. The HOMO of PFPEA additive reacts with LUMO of Fe atom to result in chemical adsorption. The LUMO of additive can interact with the SOMO of RfO. and accept electron of RfO. to form stable addition product. The additives have the property of donating-accepting electron. The electron-releasing group, particularly, the phenyl group, introduced to N atom of phenylamide can increase the combination energy and chemical adsorption energy, and enhance the antioxidant and anticorrosive efficiency. The research achi