Assignment of the 13C chemical shifts of ethidium bromide and analogs in D2O solution

The ¹³C resonances of ethidum bromide (1), dimidium bromide (2) and 3,8-diamino-5-methylphenanthridinium chloride (3) in D₂O solution have been assigned. Assignments were made using fully coupled spectra, spectra obtained from a selected 180°-τ-90° pulse sequence in conjunction with gated irradiation to obtain NOE intensification, selective proton decoupling, chemical shift arguments and by noting the effect of pD on the ¹³C chemical shifts of 1 and 3.     

Parametric integer linear programming: A synthesis of branch and bound with cutting planes

A branch and bound algorithm is designed to solve the general integer linear programming problem with parametric right-hand sides. The right-hand sides have the form b + θd where b and d are comformable vectors, d consists of nonnegative constants, and θ varies from zero to one.The method consists of first determining all possible right-hand side integer constants and appending this set of integer constants to the initial tableau to form an expanded problem with a finite number of family members. The implicit enumeration method gives a lower bound on the integer solutions. The branch and bound method is used with fathoming tests which allow one family member possibly to fathom other family members. A cutting plane option applies a finite number of cuts to each node before branching. In addition, the cutting plane method is invoked whenever some members are feasible at a node and others are infeasible. The branching and cutting process is repeated until the entire family of problem has been solved.     

Assignment of the carbon-13 chemical shifts of quinacrine,chloroquine and related compounds in D2O solution

The carbon resonances of quinacrine, chloroquine, acranil, 4-aminopyridine and 9-aminoacridine in D₂O solution have been assigned. Resonance assignments were made using empirical shift parameters, partial proton decoupling, selective proton decoupling and by interpretation of the fully coupled spectra. The effect of pD on the carbon chemical shifts for quinacrine and chloroquine over the range of about 4.5 to 8.5 was observed. Characteristic chemical shifts for the aromatic ring carbons for deprotonation of the heteroaromatic nitrogen were observed.     

Experimental study of sound propagation in a chain of spherical beads

In this paper are described experimental observations which are concerned by the propagation of pulsed ultrasonic waves transmitted through a limited one dimensional periodic granular medium submitted to a static force. This study--which is limited to a time domain analysis--exhibits experimental results which depend on the polarization of the acoustic excitation. In the case of compressional excitation, spherical Rayleigh type surface waves propagate around the beads. In the case of shear excitation, the experimental recordings point out the existence of a very low signal, the frequency of which is equal to the cut-off frequency of the chain. Moreover it is established that the frequency value varies with the radius of the bead, the normal force applied to the beads, and the mechanical properties of the material.     

A quantum chemical study of the decomposition of Keggin-structured heteropolyacids

Heterpolyacids (HPAs) demonstrate catalytic activity for oxidative and acid-catalyzed hydrocarbon conversion processes. Deactivation and thermal instability, however, have prevented their widespread use. Herein, ab initio density functional theory is used to study the thermal decomposition of the Keggin molecular HPA structure through the desorption of constitutional water molecules. The overall reaction energy and activation barrier are computed for the overall reaction HnXM12O40-->Hn-2XM12O39+H2O. and subsequently used to predict the effect of HPA composition on thermal stability. For example, the desorption of a constitutional water molecule is found to be increasingly endothermic in the order silicomolybdic acid (H4SiMo12O40)相似文献   

Identification of N-linked glycosylation sites in human nephrin using mass spectrometry

Nephrin is a type-1 transmembrane glycoprotein and the first identified principal component of the glomerular filtration barrier. Ten potential asparagine (N)-linked glycosylation sites have been predicted within the ectodomain of nephrin. However, it is not known which of these potential sites are indeed glycosylated and what type of glycans are involved. In this work, we have identified the terminal sugar residues on the ectodomain of human nephrin and utilized a straightforward and reliable mass spectrometry-based approach to selectively identify which of the ten predicted sites are glycosylated. Purified recombinant nephrin was subjected to peptide-N-glycosidase F (PNGase F) to enzymatically remove all the N-linked glycans. Since PNGase F is an amidase, the asparagine residues from which the glycans have been removed are deaminated to aspartic acid residues, resulting in an increase in the peptide mass with 1 mass unit. Following trypsin digestion, deglycosylated tryptic peptides were selectively identified by MALDI-TOF MS and their sequence was confirmed by tandem TOF/TOF. The 1 Da increase in peptide mass for each asparagine-to-aspartic acid conversion, along with preferential cleavage of the amide bond carboxyl-terminal to aspartic acid residues in peptides where the charge is immobilized by an arginine residue, was used as a diagnostic signature to identify the glycosylated peptides. Thus, nine of ten potential glycosylation sites in nephrin were experimentally proven to be modified by N-linked glycosylation.     

Synthesis and biological properties of C-2 triazolylinosine derivatives

O(6)-(Benzotriazol-1H-yl)guanosine and its 2'-deoxy analogue are readily converted to the O(6)-allyl derivatives that upon diazotization with t-BuONO and TMS-N(3) yield the C-2 azido derivatives. We have previously analyzed the solvent-dependent azide·tetrazole equilibrium of C-6 azidopurine nucleosides, and in contrast to these, the O(6)-allyl C-2 azido nucleosides appear to exist predominantly in the azido form, relatively independent of solvent polarity. In the presently described cases, the tetrazole appears to be very minor. Consistent with the presence of the azido functionality, each neat C-2 azide displayed a prominent IR band at 2126-2130 cm(-1). A screen of conditions for the ligation of the azido nucleosides with alkynes showed that CuCl in t-BuOH/H(2)O is optimal, yielding C-2 1,2,3-triazolyl nucleosides in 70-82% yields. Removal of the silyl groups with Et(3)N·3HF followed by deallylation with PhSO(2)Na/Pd(PPh(3))(4) gave the C-2 triazolylinosine nucleosides. In a continued demonstration of the versatility of O(6)-(benzotriazol-1H-yl)purine nucleosides, one C-2 triazolylinosine derivative was converted to two adenosine analogues via these intermediates, under mild conditions. Products were desilylated for biological assays. The two C-2 triazolyl adenosine analogues demonstrated pronounced antiproliferative activity in human ovarian and colorectal carcinoma cell cultures. When evaluated for antiviral activity against a broad spectrum of DNA and RNA viruses, some of the C-2 triazolylinosine derivatives showed modest inhibitory activity against cytomegalovirus.     

Photooxidation of Co-thiolato complexes in protic and aprotic solvents

Protic solvents decrease the susceptibility of the thiolate ligand in Co(III) thiolato complexes toward attack by singlet oxygen, but greatly increase the conversion of the peroxidic intermediate to the sulfenato product.