Selection of molecular chirality by extremely weak chiral interactions under far-from-equilibrium conditions

A general formalism for chiral symmetry breaking in far-from-equilibrium chemical systems is presented. It is pointed out that slow passage through the transition point makes the system sensitive to very weak, but systematic, chiral influences. The general implications of this process for the origin of biomolecular chirality is discussed.     

Emergence of molecular chirality due to chiral interactions in a biological environment

We explore the interplay between tunneling process and chiral interactions in the discrimination of chiral states for an ensemble of molecules in a biological environment. Each molecule is described by an asymmetric double-well potential and the environment is modeled as a bath of harmonic oscillators. We carefully analyze different time-scales appearing in the resulting master equation at both weak- and strong-coupling limits. The corresponding results are accompanied by a set of coupled differential equations characterizing optical activity of the molecules. We show that, at the weak-coupling limit, chiral interactions prohibit the coherent racemization induced by decoherence effects and thus preserve the initial chiral state. At the strong-coupling limit, considering the memory effects of the environment, Markovian behavior is observed at long times.     

Effects and molecular mechanisms of the biological action of weak and extremely weak magnetic fields

A number of effects of weak combined (static and alternating) magnetic fields with an alternating component of tens and hundreds nT at a collinear static field of 42 μT, which is equivalent to the geomagnetic field, have been found: activation of fission and regeneration of planarians Dugesia tigrina, inhibition of the growth of the Ehrlich ascites carcinoma in mice, stimulation of the production of the tumor necrosis factor by macrophages, decrease in the protection of chromatin against the action of DNase 1, and enhancement of protein hydrolysis in systems in vivo and in vitro. The frequency and amplitude ranges for the alternating component of weak combined magnetic fields have been determined at which it affects various biological systems. Thus, the optimal amplitude at a frequency of 4.4 Hz is 100 nT (effective value); at a frequency of 16.5 Hz, the range of effective amplitudes is broader, 150–300 nT; and at a frequency of 1 (0.5) Hz, it is 300 nT. The sum of close frequencies (e.g., 16 and 17 Hz) produces a similar biological effect as the product of the modulating (0.5 Hz) and carrying frequencies (16.5 Hz), which is explained by the ratio A = A ₀sinω₁ t + A ₀sinω₂ t = 2A ₀sin(ω₁ + ω₂)t/2cos(ω₁–ω₂)t/2. The efficiency of magnetic signals with pulsations (the sum of close frequencies) is more pronounced than that of sinusoidal frequencies. These data may indicate the presence of several receptors of weak magnetic fields in biological systems and, as a consequence, a higher efficiency of the effect at the simultaneous adjustment to these frequencies by the field. Even with consideration of these facts, the mechanism of the biological action of weak combined magnetic fields remains still poorly understood.     

Neutral currents in weak interactions and molecular asymmetry

Weak interactions are parity violating forces, i.e. they differentiate between mirror images. Therefore it is a very attractive hypothesis to invoke weak interactions in explaining the origin of molecular asymmetry. It is, however, not clear whether weak interactions may operate between electrons and/or between electrons and protons? For these types of interactions so called neutral currents are needed. Recent experiments with muon neutrinos at CERN gave some evidence for the existence of neutral currents. Thus we may suppose that parity violating forces are active in molecules. In the first part of this paper a very elementary theory of weak interactions is outlined with special reference to the discovery of neutral currents. In the second part we show how weak interactions may differentiate between mirror image molecules. The asymmetrically distributed static charges in chiral molecules represent a helical potential field. This potential field may exert an effect on the orbital electrons and therefore coupling of spins and momenta occurs. Thus the enantiomers are parity transformed images not only as geometrical bodies, but their orbital electrons are parity transformed too as "a helical electron gas". Weak interactions will differentiate between L and D forms because their orbital electrons have a nonzero spin polarization with respect to their velocity.     

Role of the weak interactions in enantiorecognition of racemic dihydropyrimidinones by novel brush-type chiral stationary phases

The chiral discrimination ability of two recently prepared chiral stationary phases (CSP 1 and CSP 2), based on a leucine derived chiral selector, was tested for the enantiomers of dihydropyrimidone (DHPM) derivatives and compared with the commercially available Hyun-leucine CSP 3 and classical Pirkle-leucine CSP 4. By combining all of these CSPs, the enantiomers of all DHPM derivatives used in this study can be properly resolved. Particularly good enantioresolutions were achieved for thioureide derivatives, such as Monastrol. The results presented show that sulfur-aromatic interactions are meritorious for these very good separations.     

The effects of weak extremely low frequency magnetic fields on calcium/calmodulin interactions.

Mechanisms by which weak electromagnetic fields may affect biological systems are of current interest because of their potential health effects. Lednev has proposed an ion parametric resonance hypothesis (Lednev, 1991, Bioelectromagnetics, 12:71-75), which predicts that when the ac, frequency of a combined dc-ac magnetic field equals the cyclotron frequency of calcium, the affinity of calcium for calcium-binding proteins such as calmodulin will be markedly affected. The present study evaluated Lednev's theory using two independent systems, each sensitive to changes in the affinity of calcium for calmodulin. One of the systems used was the calcium/calmodulin-dependent activation of myosin light chain kinase, a system similar to that previously used by Lednev. The other system monitored optical changes in the binding of a fluorescent peptide to the calcium/calmodulin complex. Each system was exposed to a 20.9 microT static field superimposed on a 20.9 microT sinusoidal field over a narrow frequency range centered at 16 Hz, the cyclotron frequency of the unhydrated calcium ion. In contrast to Lednev's predictions, no significant effect of combined dc-ac magnetic fields on calcium/calmodulin interactions was indicated in either experimental system.     

Emerging trends in molecular recognition: utility of weak aromatic interactions

Aromatic interactions play a vital role in chemistry and biology. As about 20% are aromatic in nature, so the role of aromatic interactions become prominent in drug receptor interactions. Not only in drug receptor interactions but also in crystal engineering, protein folding, stacking interactions in DNA/RNA the role of the interactions is of utmost importance. With the emergence of supramolecular chemistry dendrimers, tweezers, rotaxanes, catenanes, and several supramolecular aggregates are associated with aromatic interactions. The mechanism of such interactions is still unknown by the replacement of a small substituent from the aromatic molecule may lead or destroy the interactions. In the present review several models are being discussed with arene interactions under selected heads.     

A general criterion for molecular recognition: implications for chiral interactions

A general criterion is formulated for molecular recognition. The criterion for recognition is the inequality of the distance matrices of complexes of different compounds with a resolving agent under ambient experimental conditions. It is shown how this criterion provides for an objective, well-defined, and simple explanation for recognition of chiral compounds. This approach may be used to explain models (e.g., three-point of attachment) and relationships for chiral recognition. It is also shown how one-, two-, or three-point mechanisms are equivalent in this formalism and could result in chiral recognition. Examples are used to illustrate how the so called one- or two-point mechanisms may be operative in many experimental findings. Symmetry requirements of resolving agents may also be derived from considerations of distance matrices. Finally, the reciprocal relationship of chiral resolving agents is easily derived from the present method of analysis.     

Induced circular dichroism by chiral molecular interaction

Molecular interactions between chiral (nonracemic) and achiral compounds can give rise to induced circular dichroism (ICD) of the achiral counterpart, provided the latter absorbs in the UV or visible region under study. The CD spectra thus obtained are of interest as indicators of the absolute configuration of the chiral component, as well as of the orientation of the molecules relative to each other within the host-guest complex. The technique can provide unique information about supramolecular events, not only in solution but also in the solid state. The recent progress in the field is summarized in this brief review.     

Cell response to extremely weak static magnetic fields

The effect of an extremely weak static magnetic field (EWSMF) was studied in diploid fibroblast strains that originated from a healthy donor and an ataxia–telangiectasia patient. Indirect immunofluorescence was used to detect p53, p53BP1, and p21. The pattern that occurred in donor cells exposed to EWSMF similar to that observed in DNA damage, viz., the p53 and p21 levels increased and p3BP1 foci formed. No visible change was observed in primary fibroblasts from the ataxia–telangiectasia patient. The results implicate ATM signaling in the fibroblast response to EWSMF.     

A novel spectroscopic probe for molecular chirality

Recent advances in developing sum frequency generation (SFG) as a novel spectroscopic probe for molecular chirality are reviewed. The basic principle underlying the technique is briefly described, in comparison with circular dichroism (CD). The significantly better sensitivity of the technique than CD is pointed out, and the reason is discussed. Bi-naphthol (BN) and amino acids are used as representatives for two different types of chiral molecules; the measured chirality in their electronic transitions can be understood by two different molecular models, respectively, that are extensions of models developed earlier for CD. Optically active or chiral SFG from vibrational transitions are weaker, but with the help of electronic-vibrational double resonance, the vibrational spectrum of a monolayer of BN has been obtained. Generally, optically active SFG is sufficiently sensitive to be employed to probe in-situ chirality of chiral monolayers and thin films.     

Inhibition of growth rate of escherichia coli induced by extremely low-frequency weak magnetic fields

Cultures of Escherichia coli kept at 0 °C in a phosphate buffer solution were exposed to a sinusoidal weak 60- or 600-Hz magnetic field of strength 2 × 10^?3 Tesla. A decrease of more than 40% in bacterial count was observed after a 60-h exposure to the magnetic field. Electron micrographs of exposed bacteria show ruptured cell walls, possibly due to the breaking away of flagella under the influence of the sinusoidally varying electromotive force.     

Effect of phosphatidylcholine vesicle size on chirality induction and chiral discrimination

The effect of the size of phosphatidylcholine (PC) vesicles on the induction of chirality and chiral discrimination was examined. Three kinds of vesicles formed with l-dimyristoyl, l-dipalmitoyl, or egg yolk PCs induced circular dichroisms (CDs) with the sign and intensity of the Cotton effect different from those of monomeric PCs. The CD intensity of the vesicles increased with a decrease in the vesicle size. Furthermore, the helicity of heterohelicene derivatives in a rapid equilibrium between right-handed (P) and left-handed (M) enantiomers was biased toward the M enantiomer side in l-PC vesicles, implying chiral discrimination by the vesicles. The extent of the bias toward the M enantiomer increased with an increase in vesicle size. Both the chirality induction and chiral discrimination were enhanced in a low-fluidity gel phase in comparison with those in a high-fluidity liquid-crystalline phase for every kind of vesicle of every size examined.     

Kinetic measurements of molecular interactions by spectrofluorometry

The kinetics of antibody–antigen interactions are reviewed in terms of general trends observed in both polyclonal and monoclonal antibody populations. Anti-fluorescein antibodies are featured in the review as model proteins to explore fluorescence-based kinetic measurements. Since the fluorescence of the fluorescein ligand is significantly quenched upon interaction with both polyclonal and monoclonal anti-fluorescein antibodies, the quenching parameter can be advantageously employed in measuring the rates of association (k₁) and dissociation (k₂). The near diffusion-limited k₁ rates and the prolonged k₂ rates are discussed in terms of antibody affinity and mechanisms involved in ligand binding. Specific prolongation effects of reagents, such as anti-metatype antibodies, on the dissociation rate are discussed in terms of antibody dynamics and conformational substates.     

Investigation of Lignin-water interactions by molecular simulation

The results of molecular dynamics simulations of three lignin-water systems are presented. Static and dynamic properties of each system are compared to a benchmark system consisting entirely of water molecules. The significantly reduced mobility of water molecules local to lignin hydroxyl regions is attributed to hydrogen bond formation, while the slightly reduced mobility of water molecules in the vicinity of lignin methoxyl groups results from a hydrophobic effect that causes water molecules to structure themselves around these groups. The average diffusion of water in each system correlates with the number of methoxyl groups present in the system. As the number of methoxyls in the system increases, so too does the average diffusion constant of water in that system. The bulky methoxyl groups obstruct water from accessing lignin hydroxyl regions where hydrogen bond formation is anticipated and the hydrogen-bonded water lowers the average diffusion constant.