Investigation of the Structure and Dynamics of the Capsid–Spacer Peptide 1–Nucleocapsid Fragment of the HIV‐1 Gag Polyprotein by Solution NMR Spectroscopy

Structural studies of HIV‐1 Gag, the primary structural polyprotein involved in retroviral assembly, have been challenging, owing to its flexibility and conformational heterogeneity. Using residual dipolar couplings, we show that the four structural units of the capsid (CA)–spacer peptide 1 (SP1)–nucleocapsid (NC) fragment of HIV‐1 Gag (namely, the N‐ and C‐terminal domains of capsid, and the N‐ and C‐terminal Zn knuckles of nucleocapsid) have the same structures as their individually isolated counterparts, and tumble semi‐independently of one another in the absence of nucleic acids. Nucleic acids bind exclusively to the nucleocapsid domain and fix the orientation of the two Zn knuckles relative to one another so that the nucleocapsid domain/nucleic acid complex behaves as a single structural unit. The low ¹⁵N–{¹H} heteronuclear NOE values (≤0.4), the close to zero values for the residual dipolar couplings of the backbone amides, and minimal deviations from random‐coil chemical shifts for the C‐terminal tail of capsid and SP1, both in the absence and presence of nucleic acids, indicate that these regions are intrinsically disordered in the context of CA–SP1–NC.     

Molecular Conformations of Shape Anisometrically Variant Mesogens in Liquid Crystalline Phase Studied by 13C NMR Spectroscopy

Mesogens that vary in shape anisometry have been investigated by ¹³C solid-state NMR in the liquid crystalline phase to inspect the conformations. The molecules examined comprise of (i) rod-like mesogen with three-phenyl ring core and terminal hexyloxy chains, (ii) three-ring core linked to the fourth phenyl ring via a spacer, and (iii) trimesic acid connected to three side arms core units through a spacer. The order parameter (S_zz) values for the phenyl rings of the rod-like mesogen are 0.65–0.68, while the mesogen with a three-ring core linked to a phenyl ring via spacer showed dissimilarity. Consequently, for the core unit phenyl rings, S_zz is ~0.70, and the terminal phenyl ring showed a low value of 0.12. For the trimesic acid based mesogen, the S_zz value for the side arm phenyl rings is ~0.53, and for the central phenyl ring, a very low value of 0.11 is witnessed. By considering the ordering of the rod-like mesogen as a yardstick and employing the ratios of S_zz values of the phenyl rings, the average conformations of other mesogens are arrived. Accordingly, for the trimesic acid based mesogen, a tripod-like conformation instead of λ shape is proposed in the liquid crystalline phase.     

NMR spin-spin couplings involving nuclei in the neighborhood of a carbonyl group. 3JCH couplings in alpha-substituted acetamides

In this work 3JCH spin-spin coupling constants (SSCCs) for the cis- and trans-conformers for alpha-X-acetamides (X = F, Cl, Br and CN) (1-4) were studied in detail since they were found to be notably different for both conformers. These differences are rationalized as originating in the changes of the strong negative hyperconjugative interactions that take place within the carbonyl group. Such changes are found to depend not only on conformation, but also on solvent. For the cis-conformers there is a close proximity between the X-substituent and the in-plane oxygen lone pair of pure p character, which affects notably their respective negative hyperconjugative interactions. Both the efficiency for transmitting the Fermi contact (FC) term through the coupling pathway of 3JCH SSCCs and its potential as a probe to study the stereochemical properties of the XH2C group are discussed.     

Polyacetylenes as enantiodifferentiating alignment media

Orientation help: Valine-derived polyacetylenes are introduced as enantiomer-differentiating alignment media. The F2-coupled HSQC-type NMR spectra of both enantiomers of isopinocampheol (IPC) display narrow line widths allowing for the precise extraction of residual dipolar couplings (black contour plot: (+)-IPC in an isotropic phase, blue: (-)-IPC in an anisotropic phase, and red: (+)-IPC in an anisotropic phase; J=coupling constant).     

节点状态不同的两个耦合网络的同步

本文研究了节点动力学不同的两个耦合网络的同步,我们发现两个耦合网络之间不能达到同步,但是他们可以达到各自的同步态．利用线性化方法,我们给出了相应的定理,并用数值例子验证了理论结果．     

Self-synchronization of the integrate-and-fire pacemaker model with continuous couplings

The integrate-and-fire cardiac pacemaker model of the pulse coupled oscillators was introduced by C. Peskin. Due to the function of the pacemaker, two famous synchronization conjectures for identical and not identical oscillators were formulated. There are still many issues related to the nature and types of couplings. The couplings may be impulsive, continuous, delayed or advanced, and oscillators may be locally or globally connected. Consequently, it is reasonable to consider various ways of synchronization, if one wants the biological and mathematical analyses to interact productively. We investigate the integrate-and-fire model in both cases-one with identical, and another with not quite identical oscillators. A combination of continuous and pulse couplings that sustain the firing in unison is carefully constructed. Moreover, we obtain conditions on the parameters of continuous couplings that make possible a rigorous mathematical investigation of the problem. The technique developed for differential equations with discontinuities at non-fixed moments and a special continuous map lies on the basis of the analysis. This is the first analytically derived synchronization result for a model with continuous couplings. Illustrative examples are provided.     

多延时互耦合半导体激光器的实时混沌同步特性

针对双延时和三延时互耦合半导体激光器系统,研究了互耦合延时和互耦合强度对实时混沌同步质量的影响,提出了双延时互耦合系统中可将其中一个互耦合延时看作反馈延时的思想,揭示了多延时互耦合半导体激光器系统实时混沌同步条件和规律.研究结果表明,多延时互耦合系统中,某两条双向链路的互耦合延时比值为2,是实现高品质实时混沌同步的基本条件;增大互耦合强度,可以改善实时混沌同步品质,且在较低的等效耦合强度条件下,双延时互耦合系统较三延时互耦合系统更易于实现良好的实时混沌同步.     

Influence of the Thiophene Ring on the Molecular Order of Structurally Simple π-Conjugated Smectogens: 13C NMR Study

Structurally simple rod-like π-conjugated mesogens with thiophene directly connected to phenyl, biphenyl, and fluorenone rings with terminal chains are synthesized respectively. The occurrence of smectic A/smectic C phases is concurred by a hot-stage optical polarising microscope (HOPM), differential scanning calorimetry (DSC), and X-ray diffraction (XRD). The static 1D and 2D ¹³C nuclear magnetic resonance (NMR) studies in the liquid crystalline phase are carried out to find the alignment-induced chemical shifts (AIS) and ¹³C−¹H dipolar couplings. The orientational order parameters of the mesogens determined from ¹³C−¹H dipolar couplings disclose that the long axis is not only collinear to the C3−C4 bond of the thiophene ring but also for the local axes of phenyl and biphenyl rings. For fluorenone-based mesogen, the molecular biaxiality is found to be high owing to the increased breadth of the molecule. The study unveils that the orientation of thiophene and the phenyl rings is similar in the current mesogens in stark contrast to mesogens, where thiophene is connected to phenyl rings through linking groups.