The crystal structures at 80 K and IR spectra of the complex of 4-methylpyridine with pentachlorophenol and its deuterated analogue

The crystal structures of the complex of 4-methylpyridine with pentachlorophenol (MP-PCP) and its deuterated analogue (MP-PCP-d) were determined at 80 K by X-ray diffraction. The MP-PCP complex crystallizes in the space group P with a = 7.267(7), b = 8.966(9), c = 13.110(14)Å, = 99.70(8), β = 118.16(9), γ = 103.38(8)° and Z = 2 and the MP-PCP-d complex in the monoclinic Cc space group with a = 3.826(2), b = 27.54(2), c = 13.209(12)Å, β = 101.38(9)° and Z = 4. The O… H … N bridge bond distance of 2.515(4) Å is significantly shorter than that determined at room temperature (2.552(4) Å) and the O---D … N bond length of 2.628(6) Å is only slightly shorter than at room temperature (2.638(3) Å). The temperature dependence of the IR spectra confirms the symmetrization of the OHN hydrogen bond.     

The crystal structures at 80 K and IR spectra of the complex of 4-methylpyridine with pentachlorophenol and its deuterated analogue

The crystal structures of the complex of 4-methylpyridine with pentachlorophenol (MP---PCP) and its deuterated analogue (MP---PCP-d) were determined at 80 K by X-ray diffraction. The MP---PCP complex crystallizes in the space group with a = 7.267(7), b = 8.966(9), c = 13.110(14) Å, = 99.70(8), β = 118.16(9), γ = 103.38(8)° and Z = 2 and the MP---PCP-d complex in the monoclinic Cc space group with a = 3.826(2), b = 27.54(2), c = 13.209(12) Å, β = 101.38(9)° and Z = 4. The O…H…N bridge bond distance of 2.515(4) Å is significantly shorter than that determined at room temperature (2.552(4) Å) and the O---D…N bond length of 2.628(6) Å is only slightly shorter than at room temperature (2.638(3) Å). The temperature dependence of the IR spectra confirms the symmetrization of the OHN hydrogen bond.     

Structural Studies by NMR and X-Ray Crystallography of N-(p-Toluenesulfonyl)-Amino Acids

N-(p-Toluenesulfonyl)-glycine 7 and analogous derivatives of d,l-alanine 8, L-valine 9, L-leucine 10, L-isoleucine 11, and L-phenylalanine 12 were synthesized by condensation of the amino acid with p-toluenesulfonyl chloride. The presence of intermolecular hydrogen bonding was established by variable NMR spectroscopy. The molecular structure and intermolecular interactions of N-(p-toluenesulfonyl)–d,l-alanine and N-(p-toluenesulfonyl)–L-valine were corroborated by X-ray diffraction (XRD) experiments.     

Conformational studies of the linear homooligomers of a glucose-derived furanoid sugar amino acid

Conformational analysis of the linear tetramer of the glucose-derived furanoid sugar amino acid 1 by NMR and constrained molecular dynamics studies revealed that the fully protected tetramer 2a has a well-defined structure in CDCl₃ with repeating β-turns, each involving a 10-membered ring structure with intramolecular hydrogen bonds between NH_i → CO_i−2. Its deprotected versions 2b and 2c showed aggregation in organic solvents with structures similar to that of 2a.     

One-step preparation,structural assignment,and X-ray study of 2,2-di-n-butyl- and 2,2-diphenyl-6-aza-1,3-dioxa-2-stannabenzocyclononen-4-ones derived from amino acids

Twenty-four 2,2-di-n-butyl- and 2,2-diphenyl-6-aza-1,3-dioxa-2-stannabenzocyclononen-4-ones, each having a transannular N-->Sn bond, have been prepared by one-step reactions of alpha-amino acids (1 a-l), salicylaldehyde (2), and either di-n-butyltin(IV) oxide (3) or diphenyltin(IV) oxide (4). The new methodology constitutes an easy, highly efficient one-step synthesis of diorganotin(IV) derivatives, such as 5 a-l and 6 a-l, from iminic tridentate ligands without isolation of the Schiff bases. The structures of all the compounds have been established by a combination of (1)H, (13)C, (15)N, and (119)Sn NMR spectroscopy, IR spectroscopy, mass spectrometry, and elemental analysis. In all cases, the (119)Sn chemical shifts, as well as the (1)J((119)Sn,(13)C) coupling constants, are indicative of pentacoordinated tin atoms in solution. The structures of compounds 5 a, d, f, 6 a, b, b-racemic, c, d, f, g, and l have been established by single-crystal X-ray diffraction analyses. The tin atoms in 5 d, f, 6 a, b, b-racemic, c, d, g, and l each have a distorted trigonal-bipyramidal (TBP) geometry, with the oxygen atoms from the phenol and carboxylate moieties occupying the axial positions, and the imine nitrogen and phenyl or n-butyl substituents occupying the equatorial positions. Compounds 5 a and 6 f show distorted octahedral (DOC) geometries due to intermolecular coordination of the carbonyl oxygen to the tin atom, in a trans disposition to the N-->Sn bond, leading to trimeric 5 a and a polymeric structure for compound 6 f. Additionally, measurement of the one-bond coupling constants (1)J((119)Sn,(13)C) in diphenyltin(IV) complexes (6 a-l) and their correlation with the CSn-C bond angles has allowed the derivation of an equation that can be applied to assess the geometry around the tin atom for other diphenyltin(IV) compounds in solution.     

14N Solid‐State NMR Spectroscopy of Amino Acids

¹⁴N ultra‐wideline solid‐state NMR (SSNMR) spectra were obtained for 16 naturally occurring amino acids and four related derivatives by using the WURST–CPMG (wideband, uniform rate, and smooth truncation Carr–Purcell–Meiboom–Gill) pulse sequence and frequency‐stepped techniques. The ¹⁴N quadrupolar parameters were measured for the sp³ nitrogen moieties (quadrupolar coupling constant, C_Q, values ranged from 0.8 to 1.5 MHz). With the aid of plane‐wave DFT calculations of the ¹⁴N electric‐field gradient tensor parameters and orientations, the moieties were grouped into three categories according to the values of the quadrupolar asymmetry parameter, η_Q: low (≤0.3), intermediate (0.31–0.7), and high (≥0.71). For RNH₃⁺ moieties, greater variation in N?H bond lengths was observed for systems with intermediate η_Q values than for those with low η_Q values (this variation arose from different intermolecular hydrogen‐bonding arrangements). Strategies for increasing the efficiency of ¹⁴N SSNMR spectroscopy experiments were discussed, including the use of sample deuteration, high‐power ¹H decoupling, processing strategies, high magnetic fields, and broadband cross‐polarization (BRAIN‐CP). The temperature‐dependent rotations of the NH₃ groups and their influence on ¹⁴N transverse relaxation rates were examined. Finally, ¹⁴N SSNMR spectroscopy was used to differentiate two polymorphs of l ‐histidine through their quadrupolar parameters and transverse relaxation time constants. The strategies outlined herein permitted the rapid acquisition of directly detected ¹⁴N SSNMR spectra that to date was not matched by other proposed methods.     

蛋白质功能化新策略:嵌入非天然氨基酸

天然蛋白质由20种天然氨基酸组成,这些蛋白质的构筑基元包含功能基团:羧基、氨基、巯基、硫醚、羟基、碱性胺、烷基和芳基。然而,这些有限的功能基团却不足以完成生物体内所有的生物学功能。为了更好地让生命的体现者--蛋白质完成更加精确和多样的生物学功能,自然界会对蛋白质进行翻译后的修饰,包括:磷酸化,甲基化,乙酰化或者羟基化,甚至在某些情况下,进化出一种新型的翻译机制以便插入硒代半胱氨酸或者吡咯霉素。受此启发,生物化学家发展出各种生物或化学方法来改变或插入新的蛋白质构筑基元,使天然蛋白质完成其相应的生物学功能或者使其具有某些特殊的性质,甚至是创造一种新酶。该文将简单介绍这些蛋白质修饰策略以及该领域的最新进展。     

醇和N,N-二甲基乙酰胺分子间相互作用的FTIR光谱研究

The association between alcohols and N,N-dimethylacetamide in carbon tetrachloride was investigated using FTIR spectroscopy at 298 K.The formation constants for 1∶1 and 1∶2 complexes were calculated using the method of Whetsel and Kagarise.The observed 1∶1 complex values were also verified using the method of Nash.The rate of change in C=O bond moment on complexing with alcohols increased with increasing acidity of alcohols.The formation constant and values of free energy change increased with the increase in carbon chain length of alcohols,which suggested that the degree of complex formation varied with the length of the carbon chain of alcohols.     

A Modular Approach To Study Protein Adsorption on Surface Modified Hydroxyapatite

Biocompatible inorganic nano‐ and microcarriers can be suitable candidates for protein delivery. This study demonstrates facile methods of functionalization by using nanoscale linker molecules to change the protein adsorption capacity of hydroxyapatite (HA) powder. The adsorption capacity of bovine serum albumin as a model protein has been studied with respect to the surface modifications. The selected linker molecules (lysine, arginine, and phosphoserine) can influence the adsorption capacity by changing the electrostatic nature of the HA surface. Qualitative and quantitative analyses of linker‐molecule interactions with the HA surface have been performed by using NMR spectroscopy, zeta‐potential measurements, X‐ray photoelectron spectroscopy, and thermogravimetric analyses. Additionally, correlations to theoretical isotherm models have been calculated with respect to Langmuir and Freundlich isotherms. Lysine and arginine increased the protein adsorption, whereas phosphoserine reduced the protein adsorption. The results show that the adsorption capacity can be controlled with different functionalization, depending on the protein–carrier selections under consideration. The scientific knowledge acquired from this study can be applied in various biotechnological applications that involve biomolecule–inorganic material interfaces.