Gel-permeation chromatography and cellulose. I. Effect of degree of nitration of cellulose on molecular weight distribution data

Consideration is given to the effect on gel-permeation chromatographic (GPC) data of the extent of substitution in nitrated cellulose. GPC parameters for samples containing 13.55–13.81% nitrogen (14.14% corresponds to complete substitution, DS = 3) were hardly affected by this variation in substitution. Variations that were observed are considered to arise within the samples themselves. Experiments with low molecular weight organic iodides, nitrates, and hydroxyl compounds indicate longer chain lengths than actual; this is attributed to extensive solvation of the substituent groups. The very long chain lengths obtained for cellulose nitrate by the present GPC procedure may arise from such an affect.     

A weight-function approach for determining watershed initial conditions for combustion waves

In many generic combustion models, one finds that a combustionwave will develop with a specific wave speed. However, thereare possible initial temperature profiles which do not evolveinto such waves, but rather die out to the ambient temperature.There can exist, in some models, a clear distinction betweenthose initial conditions that do evolve into combustion wavesand those that do not; this is sometimes referred to as thewatershed initial condition. When fuel consumption is consideredto be negligible, analytical methods can be used to obtain theexact watershed. In this paper, we consider the problem of determiningpseudo-watersheds and ascertaining the relationship betweenthese pseudo-watersheds and the exact watersheds. In the processa novel weight-function approach for infinite spatial domainsis developed.     

Die Entflammbarkeit von mit Indigo-Farbstoffen gef?rbten Baumwoll-Geweben

Ohne Zusammenfassung     

Synthesis of cytotoxic cyanobactin,Wewakazole B

We report herein the synthesis of cytotoxic cyanobactin, Wewakazole B through an efficient solution-phase approach. The key steps of the synthesis are the macrocyclic lactamization of linear dodecapeptide and construction of two hexapeptides with three different substituted oxazole rings.     

A High-Performance Liquid Chromatography Study of D-Cellobiose Degradation Under Fenton Conditions

Abstract

Cellobiose was used to model chemical processes taking place during the weathering of cotton fiber cellulose. High-performance liquid chromatography (HPLC) showed that the products of cellobiose degradation were D-glucose and organic acids under Fenton-type conditions (ferrous ion plus H₂0₂). Hydrogen peroxide was added directly or photochemically generated in situ by the action of UV light upon aqueous ferrous ammonium sulfate. Effects on D-cellobiose degradation caused by added peroxide or ferrous ion were nonitored at varying concentrations and under UV light and dark conditions. Increasing concentrations of peroxide or ferrous ion resulted in greater degradation. Samples exposed to UV light (350 nm) experienced greater degradation than those not exposed.     

Gel permeation chromatography and cellulose. II. Application of universal calibration

In previously reported work concerning the chain-length distributions obtained by gel permeation chromatography (GPC) in celluloses, degrees of polymerization (DP) of unusually high magnitude were reported. Later work in GPC has shown that the concept of relating extended nolecular chain length of different polymers to elution volume for obtaining molecular weight is not theoretically sound. Correlation of molecular hydrodynamic volume (indicated by the product of intrinsic viscosity and molecular weight) with elution volume has been found to place polymers of vastly different natures on a single curve, such is now designated universal calibration. Application of universal calibration to the determination of DP distributions in celluloses required a different method of converting counts to DP. This new procedure is described in detail. Weight-average DP's given by the procedure for samples of cellulose I, II, III, and IV were 5190, 4520, 4795, and 3390, respectively. These are decreases of 74–75% from the results obtained by the extended-chain procedure. The results compare favorably with the viscosity-DP's of the samples. Number-average DP's were 1580, 1040, 1140, and 490 for the four samples, respectively, these being decreases of 87–93% from the values formerly reported. The polymolecularity ratios for the samples are now unusually large, being 3.4, 4.7, 4.2, and 7.1, respectively.     

Catalysis of Kumada-Tamao-Corriu coupling by a (POCOP)Rh pincer complex

A pincer-based (P(O)C(O)P)Rh catalyst is demonstrated to be an active and well-defined catalyst for the coupling of select aryl and alkyl Grignards with aryl iodides. The proposed intermediacy of oxidative addition of aryl halides to (P(O)C(O)P)Rh(I) is supported by the isolation of the oxidative addition product.