Re-Evaluation of the Activity Coefficients of Aqueous Hydrochloric Acid Solutions up to a Molality of 2.0 Using Two-Parameter Hückel and Pitzer Equations. Part I. Results at 25°C

Simple two-parameter Hückel and Pitzer equations were used for the calculation of the activity coefficients of aqueous hydrochloric acid at 25°C up to a molality of 2.0 mol-kg^–1. The data obtained by Harned and Ehlers^(12,13) from galvanic cells without liquid junction were used in the analysis and the parameters obtained were compared to those obtained from all reliable data presented in the literature for HCl at this temperature. A good agreement between the parameters was always observed. The activity coefficients obtained by the new equations were compared to those suggested by Robinson and Stokes,⁽⁸⁾ Hamer and Wu,⁽¹⁾ and Pitzer and Mayorga,⁽⁹⁾ and good agreement was also found. The data from the most important literature data sets for HCl were also predicted using the new activity coefficient equations, and the magnitude of the resulting errors was close to the precision of the measurements, the errors forming an almost random pattern for all data sets.     

Photolysis of hexamethyldisilane at 206 nm

The photolysis of Me₆Si₂ at 206 nm results in two main decomposition processes: simple Si---Si bond breaking with a quantum yield of Φ = 0.21 ± 0.03, and Me₃SiH elimination with the concomitant formation of Me₂SiCH₂ with Φ = 0.18 ± 0.01. There is also a minor decomposition channel with a very small quantum yield, Φ = (5.6 ± 0.2) × 10⁻³, which results in the formation of Me₄Si and Me₂Si. The main fate of the excited Me₆Si₂ molecule produced during photolysis is stabilization by collisional deactivation. The end products observed indicate that the reaction pathways followed by the main intermediates, Me₃Si and Me₂SiCH₂, are the same as those found in the photolysis of Me₄Si (Ahmed et al., J. Photochem. Photobiol. A: Chem. 86 (1995) 33).     

Characterization of amyloidogenic immunoglobulin light chains directly from serum by on-line immunoaffinity isolation

Primary systemic amyloidosis (AL) is characterized by the overproduction of immunoglobulin light chain proteins by a monoclonal, terminally differentiated B-lymphocyte or plasma cell clone. The free immunoglobulin light chains are deposited in an abnormal conformation as amyloid in a variety of organs in the body. The mechanism of amyloid formation is not well understood, but appears to be associated with some form of cleavage of the immunoglobulin light chain with subsequent aggregate formation. In an attempt to characterize the structure of amyloid-forming light chain proteins we developed an on-line immunoaffinity purification and subsequent characterization of free kappa and free lambda immunoglobulin light chains by electrospray ionization mass spectrometry. The methodology is totally automated and requires 20 micro L of serum. Mass spectral analysis of Bence Jones proteins under non-denaturing conditions was also utilized to examine the tertiary and quaternary structure of light chain proteins and clearly shows covalent dimer formation of lambda type light chain. This type of on-line assay may prove helpful in elucidating distinguishing features capable of discriminating AL from benign monoclonal gammopathies of undetermined significance as well as diagnosing AL.     

Synthesis of pyrimido[4,5-e][1,4]oxazepin-5-ones

Eighteen novel pyrimido[4,5-e][1,4]oxazepin-5-ones were prepared directly via the reaction of either ethyl 4-chloro-2-phenyl-5-pyrimidinecarboxylate (Ia) or ethyl 4-chloro-2-m-chlorophenyl-5-pyrimidinecarboxylate (Ib) with a variety of substituted 2-(alkylamino)ethanols. A typical example was the preparation of 8,9-dihydro-9-methyl-2-phenylpyrimido[4,5-e][1,4]-oxazepin-5(7H)-one (IIa) from the reaction of Ia with 2-(methylamino)ethanol. Hydrolytic cleavage of the lactone ring in IIa with sodium hydroxide solution, followed by acidification with hydrochloric acid afforded 4-[(2-hydroxyethyl)methylamino]-2-phenyl-5-pyrimidinecarboxylic acid (IV). Reactions of IIa with concentrated ammonium hydroxide or hydrazine also caused cleavage of the lactone ring, giving the corresponding amide (V) or hydrazide (VI), respectively. Structural assignments were supported by infrared and nuclear magnetic resonance spectra.     

Thieno[2,3-d]pyrimidines. I. A new method for the preparation of esters and amides of thieno[2,3-d] pyrimidine-6-carboxylic acids

A novel method for the preparation of esters and amides of thieno[2,3-d]pyrimidine-6-carb-oxylic acids was described. A typical example was the direct formation of ethyl 5-amino-2-methylthiothieno[2,3-d]pyrimidine-6-earboxylate(IIIa) from 4-chloro-2-methylthio-5-pyrimidine-carbonitrile (Ia) and ethyl mercaptoacetate in refluxing ethanol containing sodium carbonate. Displacement of the methylthio group in IIIa by various amines gave the corresponding amino derivatives. The reactions of IIIa and related compounds with acetylating agents such as acetic anhydride or chloroacetyl chloride gave various products. Treatment of 5-carbethoxy-4-chloro-2-phenylpyrimidine(IV) with methyl mercaptoacetate afforded the dechloro intermediate diester Va, which cyclized on reaction with sodium ethoxide to form methyl 5-hydroxy-2-phenylthieno-[2,3-d]pyrimidine-6-carboxylate (Vla). The synthesis was expanded to include the preparation of various new 2,4,5-trisubstituted thieno[2,3-d]pyrimidine-6-carboxylic acid esters and amides (Charts I-V).     

Mixed nitrosyl/phosphinidene and nitrene/phosphinidene clusters of ruthenium

Reaction of the aminophosphinidene complex [Ru5(CO)15(mu 4-PNPri2)] 1 with [PPN][NO2] (PPN = Ph3P=N=PPh3) led to the mixed nitrosyl/phosphinidene cluster complex [PPN][Ru5(CO)13(mu-NO)(mu 4-PNPri2)] 2 which is transformed into the novel nitrene/phosphinidene cluster [Ru5(CO)10(mu-CO)2(mu 3-CO)(mu 4-NH)(mu 3-PNPri2)] 3 via treatment with triflic acid.     

Sensitive o-toluidine reagent for glucose assay at moderately elevated temperatures

A reagent is developed for increasing the sensitivity of the direct o-toluidine procedure for glucose so that the reaction may be carried out at temperatures as low as 37 °C.The sensitivity is achieved by eliminating all water from the system, except for a minute percentage introduced with the samples and by using a high boric acid concentration. Under these conditions protein does not precipitate and lipids remain dissolved. At 55 °C, interference from bilirubin at a concentration of 20 mg/100 ml is 3.5%.Blood may be collected with sodium fluoride since it does not interfere in the procedure. The rate of color development is slower for aqueous standards than it is for serum at the lower temperatures. This may be corrected by preparing the standards in a 6% albumin solution.Results obtained by applying the reagent with the continuous flow system of analysis (Technicon), and with the discrete sample analyzers, Beckman DSA, Lars Jungberg Autolab (Sweden), Robot Chemist, and RaBA (Japan) are reported.The reagent is useful as a spray reagent for sugar identification on thin-layer chromatography plates. Heating at different temperatures permits the differentiation between certain sugars with similar R_f values.     

Stability and Structure of Activated Macrocycles. Ligands with Biological Applications

Single p-toluic acid pendant groups were attached to 1,4,7,10,13-pentaazacyclopentadecane (15aneN5) and 1,4,8,11-tetraazacyclotetradecane (cyclam) to prepare bifunctional reagents for radiolabeling monoclonal antibodies with (64,67)Cu. The ligands are 1,4,7,10,13-pentaazacyclopentadecane-1-(alpha-1,4-toluic acid) (PCBA) and 1,4,8,11-tetraazacyclotetradecane-1-(alpha-1,4-toluic acid) (CPTA). For the parent macrocycles and their pendant arm derivatives, the 1:1 Cu(2+) complexes dissociate only below pH 2. At pH 0.0 and 25 degrees C the CPTA-Cu complex has a half-life toward complete dissociation of 24 days. A new approach was developed for the estimation of the Cu(2+) stability constant for the kinetically robust CPTA. All other formation constants were determined at 25.0 degrees C with batch spectrophotometric techniques. Potentiometric titrations were used to determine the protonation constants of the macrocyclic ligands as well as of the metal chelates. The protonation constants, stability constants, and pM's are discussed in terms of both molecular mechanics calculations and the ligands' potential applicability as copper(II) radiopharmaceuticals.     

Time-resolved intraband electronic relaxation dynamics of Hg(n) (-) clusters (n=7-13,15,18) excited at 1.0 eV

Time-resolved photoelectron imaging has been used to study the relaxation dynamics of small Hg(n) (-) clusters (n=7-13,15,18) following intraband electronic excitation at 1250 nm (1.0 eV). This study furthers our previous investigation of single electron, intraband relaxation dynamics in Hg(n) (-) clusters at 790 nm by exploring the dynamics of smaller clusters (n=7-10), as well as those of larger clusters (n=11-13,15,18) at a lower excitation energy. We measure relaxation time scales of 2-9 ps, two to three times faster than seen previously after 790 nm excitation of Hg(n) (-), n=11-18. These results, along with size-dependent trends in the absorption cross-section and photoelectron angular distribution anisotropy, suggest significant evolution of the cluster anion electronic structure in the size range studied here. Furthermore, the smallest clusters studied here exhibit 35-45 cm(-1) oscillations in pump-probe signal at earliest temporal delays that are interpreted as early coherent nuclear motion on the excited potential energy surfaces of these clusters. Evidence for evaporation of one or two Hg atoms is seen on a time scale of tens of picoseconds.