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N Zumbulyadis

Publications and source records attributed to N Zumbulyadis.

10 recordsLinked to original sources
PubMed1998

Elucidation of the chain conformation in a glassy polyester, PET, by two-dimensional NMR

The chain conformation of glassy poly(ethylene terephthalate) (PET) was characterized by two-dimensional double-quantum nuclear magnetic resonance (NMR). In amorphous carbon-13-labeled PET, the statistics of the O-13CH2-13CH2-O torsion angle were determined, on the basis of the distinct shapes of the two-dimensional NMR patterns of trans and gauche conformations. In crystalline PET, the trans content is 100 percent, but in the amorphous PET it is only 14 percent (+/-5 percent). An average gauche torsion angle of 70 degrees (+/-9 degrees) was obtained. Implications for materials properties of polyesters are discussed.

Journal Article↗
PubMed1995

A simple model for deuterium cross-polarization magic-angle spinning nuclear magnetic resonance at the interphases of amorphous materials.

The structure and composition of the interphase at the boundary of two immiscible phases has long been the subject of experimental and theoretical studies in polymer science. Cross-polarization between protons and deuterons offers the potential for elucidating the composition of the interphase if one of the immiscible phases is deuterated. A prerequisite for such an analysis is the establishment of an experimental protocol for reliable spin counting in 1H-2H cross-polarization magic-angle spinning (CP-MAS) spectroscopy. In this paper we present a simple model for the quantitative analysis of deuterium CP-MAS spectra. The model will be applied to the characterization of the polystyrene-b-poly(methyl methacrylate) interphase in a subsequent publication.

Deuterium↗
PubMed1992

EPR and 1H and 13C dynamic nuclear polarization studies of a molecularly doped polymer: bisphenol A polycarbonate doped with trianisylamine and trianisylaminium perchlorate.

We have investigated the EPR and DNP behavior of a molecularly doped polymer modeling those used to transport electronic charge in electrophotography. The EPR spectra show no evidence of the superexchange reported for a closely related system based on tri-p-tolylamine. The difference may be due to larger charge-transfer matrix elements in the latter system. An unambiguous interpretation of the observed 1H DNP was rendered difficult by the unanticipated asymmetry of the EPR spectra. We report extensive data on the "three-spin" effect evident in the DNP-enhanced 13C NMR spectra, and comment on its potential for characterizing polymer interfaces.

Aniline Compounds↗
PubMed1982

Sodium ion binding in human serum.

The amount of sodium ion binding in human sera and in dialyzed human sera was estimated from standard-addition titrations with an ion-selective electrode and from measurements of 23Na nuclear magnetic resonance (NMR) linewidth. For the untreated sera, maximum binding was 1% (1.4 mmol/L) as indicated by NMR; virtually no binding was found via the titration method. For dialyzed sera with low-sodium, normal-protein content, NMR indicated that sodium binding was less than 1.3% (0.14 mmol/L). The same dialyzed fluid analyzed with ion-selective electrodes shows no sodium binding, within the limits of experimental error (+/- 4%). Sodium ion binding to serum protein thus contributes only minimally to differences in sodium measurements observed between the direct (undiluted) ion-selective electrode and flame-photometric methods.

Blood Proteins↗
PubMed1980

Human conjugated bilirubin--isolation, biosynthesis, and direct molecular characterization.

We prepared human conjugated bilirubin by isolation from fresh gall bladder bile and by biosynthesis using liver homogenates. The isolation protocol was modified after Lucassen (doctoral thesis, Univ. Utrecht, 1961), and the in vitro synthesis was done with fresh liver homogenates in the presence of D-glucaro-1,4-lactone (a glucuronidase inhibitor). From direct analyses of these preparations with 270-MHz proton nuclear magnetic resonance and field-desorption mass spectrometry, we deduced that a major conjugated bilirubin species in bile is a diglucuronide, whereas in liver biosynthesis it is a diconjugate containing glucuronic acid and possibly glucuronolactone co-esterified to the bilirubin backbone. If the glucuronolactone is indeed present in the native biosynthetic material, we do not know whether it derives from glucuronic acid and, if so, whether lactonization occurs before or after the acid has been esterified to form the conjugate.

Bile↗
PubMed1979

Proton and carbon-13 nuclear magnetic resonance studies of rhodopsin-phospholipid interactions.

Proton and carbon-13 nuclear magnetic resonance (1H and 13C NMR) spectra of rhodopsin-phospholipid membrane vesicles and sonicated disk membranes are presented and discussed. The presence of rhodopsin in egg phosphatidylcholine vesicles results in homogeneous broadening of the methylene and methyl resonances. This effect is enhanced with increasing rhodopsin content and decreased by increasing temperature. The proton NMR data indicate the phospholipid molecules exchange rapidly (less than 10(-3) s) between the bulk membrane lipid and the lipid in the immediate proximity of the rhodopsin. These interactions result in a reduction in either or both the frequency and amplitude of the tilting motion of the acyl chains. The 13C NMR spectra identify the acyl chains and the glycerol backbone as the major sites of protein lipid interaction. In the disk membranes the saturated sn-1 acyl chain is significantly more strongly immobilized than the polyunsaturated sn-2 acyl chain. This suggest a membrane model in which the lipid molecules preferentially solvate the protein with the sn-1 chain, which we term an edge-on orientation. The NMR data on rhodopsin-asolectin membrane vesicles demonstrate that the lipid composition is not altered during reconstitution of the membranes from purified rhodopsin and lipids in detergent.

Animals↗
PubMed1977

Light-regulated permeability of rhodopsin:egg phosphatidylcholine recombinant membranes.

Purified rhodopsin was incorporated into phospholipid bilayers of egg phosphatidylcholine to give recombinant membrane vesicles, which were examined by proton and phosphorus nuclear magnetic resonance spectroscopy. Increased rhodopsin content in the membranes appears to progressively inhibit the molecular motions of the methyl, methylene, and phosphate groups of the phospholipid molecules. This indicates that regions of the rhodopsin molecule interact in a manner that affects the phospholipids from the aqueous interface to the bilayer midline. In the dark, the recombinant vesicles were sealed to europium, manganese, or cobalt ions. Light exposure allowed rapid equilibration of Mn2+ and Co2+, and somewhat slower equilibration of Eu3+ across the membrane. Light changed the membrane permeability, and the gradient in chemical potential resulted in a net ion movement across the rhodopsin:phospholipid recombinant membrane. The results suggest rhodopsin is a transmembrane protein.

Cobalt↗
PubMed1976

Proton relaxation and charge accumulation during oxygen evolution in photosynthesis.

The water proton spin-spin (transverse) relaxation rate of chloroplast suspensions has been measured after each of a series of 2.4 musec light flashes. The sequence of relaxation rates shows a damped oscillatory pattern with a period of four and peaks after the 3rd, 7th, 11th, and 15th flashes. This result indicates that water proton relaxation can be used to monitor the charge-accumulating states as postulated by Kok and coworkers for the oxygen-evolving mechanism in green plants [(1970) Photochem. Photobiol. 11, 457-475]. Other experiments [Wydrzynski et al. (1975) Biochim. Biophys. Acta 408, 349-354] have shown that the proton relaxation rate is strongly influenced by membrane-bound manganese in various oxidation states, suggesting that manganese participates in the charge accumulation process during oxygen evolution.

Journal Article↗
PubMed1975

Water proton relaxation as a monitor of membrane-bound manganese in spinach chloroplasts.

First measurements of proton relaxation on chloroplast membranes are presented here. Experiments show that the water proton spin-lattice relaxation rate in chloroplast thylakoid membrane suspensions can be used to monitor membrane-bound manganese. The relaxation effect is reduced to 0.4 of its original value upon manganese extraction by washing with either alkaline Tris buffer or NH2OH/EDTA solution. Large increases in the proton relaxation rate are measured in the presence of reductants such as tetraphenylboron and NH2OH; oxidants such as potassium ferricyanide or 2,6-dichlorophenolindophenol lead to an decrease in this rate. These results suggest that manganese exists as a mixture of oxidation states in dark-adapted chloroplasts.

2,6-Dichloroindophenol↗