结构声强技术测量墙体结构中弯曲波耦合功率流

虽然结构声强技术已成功地应用于匀质薄壁结构，但在建筑结构的应用研究只是一些定性的探讨，本文应用结构声强技术研究建筑结构中弯曲波声强的测量，以传统方法获得的结构总损耗能量测量值为参考，基于９５％合成置信区间研究弯曲波声强的测量精度，初步探讨了结构声强技术在建筑中应用的可行性。     

Prediction of ortho(β) 13C chemical shifts in conjugated systems

An equation has been developed which relates ortho or C-β ¹³C substituent chemical shifts (SCS) to the ortho proton–proton coupling constant in the unsubstituted member of a conjugated series. This method is an extension of previous equations which have been used to predict ortho ¹H SCS values, and has its origin in a relationship between bond order and SCS values. The equation was derived from ortho ¹³C data in 2-naphthalenes and monosubstituted benzenes and its application to other unsaturated series is discussed.     

Polylogarithms,functional equations and more: The elusive essays of William Spence (1777–1815)

The little-known Scottish mathematician William Spence was an able analyst, one of the first in Britain to be conversant with recent continental advances, and having original views. His major work on “logarithmic transcendents” gives the first detailed account of polylogarithms and related functions. A theory of algebraic equations was published just after his early death; and further essays, edited by John Herschel, were published posthumously. The most substantial of these concern an extension of his work on “logarithmic transcendents”, and the general solution of linear differential and difference equations. But awareness of Spence?s works was long delayed by their supposed unavailability. Spence?s life, the story of his “lost” publications, and a summary of all his essays are here described.     

α-Conotoxin ImI incorporating stable cystathionine bridges maintains full potency and identical three-dimensional structure

The two disulfide bonds of α-conotoxin ImI, a peptide antagonist of the α7 nicotinic acetylcholine receptor (nAChR), were systematically replaced with isosteric redox-stable cystathionine thioethers. Regioselective thioether formation was accomplished on solid support through substitution of a γ-chlorohomoalanine by an intramolecular cysteine thiol to produce hybrid thioether/disulfide analogues (2 and 3) as well as a dual cystathionine analogue (4) that were found to be structurally homologous to α-conotoxin ImI by (1)H NMR. The antagonistic activity at the α7 nAChR of cystathionine analogue 3 (pIC(50) = 6.41 ± 0.09) was identical to that of α-conotoxin ImI (1, pIC(50) = 6.41 ± 0.09), whereas those of 2 (pIC(50) = 5.96 ± 0.09) and 4 (pIC(50) = 5.89 ± 0.09) showed a modest decrease. The effect of oxidation of the thioethers to sulfoxides was also investigated, with significant changes in the biological activities observed ranging from a >30-fold reduction (2S═O) to a 3-fold increase (3S═O(B)) in potencies.     

Design, synthesis, and characterization of a single-chain peptide antagonist for the relaxin-3 receptor RXFP3

Relaxin-3 is a two-chain disulfide-rich peptide that is the ancestral member of the relaxin peptide family and, together with its G protein-coupled receptor RXFP3, is highly expressed in the brain. Strong evolutionary conservation of relaxin-3 suggests a critical biological function and recent studies have demonstrated modulation of sensory, neuroendocrine, metabolic, and cognitive systems. However, detailed studies of central relaxin-3-RXFP3 signaling have until now been severely hampered by the lack of a readily available high-affinity antagonist for RXFP3. Previous studies have utilized a complex two-chain chimeric relaxin peptide, R3(BΔ23-27)R/I5, in which a truncated relaxin-3 B-chain carrying an additional C-terminal Arg residue was combined with the insulin-like peptide 5 (INSL5) A-chain. In this study we demonstrate that, by replacing the native Cys in this truncated relaxin-3 B-chain with Ser, a single-chain linear peptide of 23 amino acids that retains high-affinity antagonism for RXFP3 can be achieved. In vivo studies demonstrate that this peptide, R3 B1-22R, antagonized relaxin-3/RXFP3 induced increases in feeding in rats after intracerebroventricular injection. Thus, R3 B1-22R represents an excellent tool for biological studies probing relaxin pharmacology and a lead molecule for the development of synthetically tractable, single-chain RXFP3 modulators for clinical use.     

Peptide length and leaving-group sterics influence potency of peptide phosphonate protease inhibitors

The ability to follow enzyme activity in a cellular context represents a challenging technological frontier that impacts fields ranging from disease pathogenesis to epigenetics. Activity-based probes (ABPs) label the active form of an enzyme via covalent modification of catalytic residues. Here we present an analysis of parameters influencing potency of peptide phosphonate ABPs for trypsin-fold S1A proteases, an abundant and important class of enzymes with similar substrate specificities. We find that peptide length and stability influence potency more than sequence composition and present structural evidence that steric interactions at the prime-side of the substrate-binding cleft affect potency in a protease-dependent manner. We introduce guidelines for the design of peptide phosphonate ABPs and demonstrate their utility in a live-cell labeling application that specifically targets active S1A proteases at the cell surface of cancer cells.     

Native peptide folding dominates over stereoelectronic effects of prolyl hydroxylation in loop 5 of the macrocyclic peptide kalata B1

Kalata B1 (4) is a prototypical, 29-residue, Möbius cyclotide with a cis prolyl peptide bond in loop 5. Two analogs were synthesized in which Pro²⁴ was substituted by trans-4-hydroxy-l-proline (peptide 5) and cis-4-hydroxy-l-proline (peptide 6). Linear peptides were assembled by solid phase peptide synthesis using Fmoc/tBu chemistry. Head-to-tail cyclization was performed using HATU, side-chain protecting groups removed and the cyclic peptides 2 and 3 isolated by RP-HPLC. Oxidation led to the formation of peptides 5 and 6, each incorporating three disulfide bonds. Analysis of TOCSY and NOESY spectra of the purified peptides enabled assignment of the backbone amide and Hα resonances. These showed a striking correlation with those of native kalata B1, indicating that folding had produced the same disulfide bridge topology. While somewhat surprising that stereoelectronic effects introduced by the hydroxyl substituents in this key region of the peptide had little impact, this reflects the strong thermodynamic driving force toward formation of the cyclic cystine knot scaffold.     

Chemical Synthesis, 3D Structure,and ASIC Binding Site of the Toxin Mambalgin‐2

Mambalgins are a novel class of snake venom components that exert potent analgesic effects mediated through the inhibition of acid‐sensing ion channels (ASICs). The 57‐residue polypeptide mambalgin‐2 (Ma‐2) was synthesized by using a combination of solid‐phase peptide synthesis and native chemical ligation. The structure of the synthetic toxin, determined using homonuclear NMR, revealed an unusual three‐finger toxin fold reminiscent of functionally unrelated snake toxins. Electrophysiological analysis of Ma‐2 on wild‐type and mutant ASIC1a receptors allowed us to identify α‐helix 5, which borders on the functionally critical acidic pocket of the channel, as a major part of the Ma‐2 binding site. This region is also crucial for the interaction of ASIC1a with the spider toxin PcTx1, thus suggesting that the binding sites for these toxins substantially overlap. This work lays the foundation for structure–activity relationship (SAR) studies and further development of this promising analgesic peptide.     

A proportional view: The mathematics of James Glenie (1750–1817)

The mathematical work of James Glenie (1750–1817) was published at irregular intervals during a turbulent life. His ideas, mostly deriving from his time as an Assistant in Mathematics at St Andrews University in Scotland, were developed intermittently over a period of thirty-seven years. His mathematical achievements, underestimated by previous historians, were deeply rooted in Euclidean geometry and his own generalized theory of proportion. Among them are many new geometrical constructions and proofs, a novel demonstration of the binomial theorem, and an alternative approach to the differential calculus.