The use of derivatives for establishing integration limits of chromatographic peaks

Summary The paper deals with composite peaks in which the resolution is not sufficient to allow simple area determinations with conventional integrator procedures. It is proposed to use the second derivatives of composite peaks, since the derivatives accentuate envelope perturbations due to overlapped peaks. In particular, when there are two solutes in the composite, and when the peak separation is between 2 and 4σ, the second derivative of the composite has two minima and three maxima. The second maximum is indicative of the cross point of the two solutes. This point can be used to initiate and/or terminate the integration of the components in the composite. Similarly, the second minimum occurs at a point close to the true maximum of the second peak in the composite. This point can also be used for the quantitative determination of the second component in the composite. The second derivative traces can also be integrated, but their utility in quantitative analysis of the peaks is questionable. An inversion procedure is given in which the second derivative trace is inverted to yield a trace similar to the conventional chromatograms but with better apparent resolution. In special circumstances, the inverted derivatives can be used for integration purposes.     

Relationship of the crystal structure of γ-N,N-dimethylaminopropyl 2,2-diphenylpropionate hydrochloride to antimuscarinic activity

The title compound was synthesized, characterized by¹H nmr, and crystallized for x-ray crystallography. The antimuscarinic potency of the title compound was about equipotent to aprophen or atropine in inhibiting acetylcholine-induced contraction of guinea pig ileum (K _B =4.5 nM) and in inhibiting carbachol-stimulated release of-amylase from rat pancreatic acinar cells (K _i =1.4nM), and in inhibiting the binding of [N-methyl-³H]scopolamine to cerebral cortex (K _i =6.6nM). In the crystal, the O-C-C-C-N⁺ segment adopted a gauche-gauche configuration resulting in an N⁺O (carbonyl) distance of 5.001(9)Å, a distance comparable to that in aprophen. The ether oxygen atom is buried rendering it inaccessible for interaction with the muscarinic receptor. The carbonyl oxygen atom is exposed to the surface of the molecule and is readily accessible for intermolecular interactions. The similarity in biological activities of the title compound and aprophen is congruous with their similar N⁺O (carbonyl) distances.National Research Council Senior Associate, on leave from the Department of Organic Chemistry, Israel Institute for Biological Research, Ness Ziona, Israel.National Research Council Senior Associate, on leave from the Department of Pharmaceutical Chemistry, Hebrew University of Jerusalem, Jerusalem, Israel.     

A new approach to high temperature photoresists based on styrylpyridinium units

Four linear polyesters containing styrylpyridinium units were prepared from 2,6-bis(p-hydroxystyryl)pyridine and terephthalic acid, isophthalic acid, adipic acid, and sebacic acid, respectively. The polyesters are thermally stable in the 365 to 450°C range. The decomposition temperature is higher for aromatic polyesters, lower for their aliphatic analogs. The polyesters are photoreactive and crosslink on irradiation with UV. The crosslinking mechanism is 2 + 2 cycloaddition. The polyesters form protonated complexes with CF₃COOH which absorb at longer wavelengths and are also photoreactive. The quantum yield of the photoreaction and the relative photosensitivities of the polyesters and their complexes were determined.     

Atomically Dispersed Molybdenum Catalysts for Efficient Ambient Nitrogen Fixation

NH₃ synthesis by the electrocatalytic N₂ reduction reaction (NRR) under ambient conditions is an appealing alternative to the currently employed industrial method—the Haber–Bosch process—that requires high temperature and pressure. We report single Mo atoms anchored to nitrogen‐doped porous carbon as a cost‐effective catalyst for the NRR. Benefiting from the optimally high density of active sites and hierarchically porous carbon frameworks, this catalyst achieves a high NH₃ yield rate (34.0±3.6 μg h^?1 mg_cat.^?1) and a high Faradaic efficiency (14.6±1.6 %) in 0.1 m KOH at room temperature. These values are considerably higher compared to previously reported non‐precious‐metal electrocatalysts. Moreover, this catalyst displays no obvious current drop during a 50 000 s NRR, and high activity and durability are achieved in 0.1 m HCl. The findings provide a promising lead for the design of efficient and robust single‐atom non‐precious‐metal catalysts for the electrocatalytic NRR.     

Modification of PET with sterically hindered diols

Poly(ethylene terephthalate) was modified by incorporating bis(hydroxyethyl) tetrasubstituted terephthalates (methyl, chlorine, and bromine) as a third component in the mole ratios of 2–50% (based on dimethyl terephthalate) which resulted in random copolyesters. The presence of steric hindrance imparted additional chain rigidity to the copolymer structure, as shown by increased glass transition temperature (T_g). The effectiveness of the steric groups for conferring rigidity to the copolymer structure was CH₃ > Cl?Br. The copolyesters which contained halogen substituents showed substantial enhancement in flame retardency compared with PET.     

Chemical reaction dynamics within anisotropic solvents in time-dependent fields

The dynamics of low-dimensional Brownian particles coupled to time-dependent driven anisotropic heavy particles (mesogens) in a uniform bath (solvent) have been described through the use of a variant of the stochastic Langevin equation. The rotational motion of the mesogens is assumed to follow the motion of an external driving field in the linear response limit. Reaction dynamics have also been probed using a two-state model for the Brownian particles. Analytical expressions for diffusion and reaction rates have been developed and are found to be in good agreement with numerical calculations. When the external field driving the mesogens is held at constant rotational frequency, the model for reaction dynamics predicts that the applied field frequency can be used to control the product composition.     

Carbamoylphosphonates part 7. An efficient method for the synthesis of hindered carbamoylphosphonates using 4-nitrophenoxycarbonylphosphonate diesters

Hindered primary amines that resist other reagents can be converted to carbamoylphosphonates by means of 4-nitrophenoxycarbonylphosphonate diesters in high yields and under mild conditions.