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S Cohen

Publications and source records attributed to S Cohen.

At least 667 records · Page 37Linked to original sources
PubMed1986

Theoretical derivation of solute-solvent interaction parameter in binary solution: case of the deviation from Raoult's law.

In a binary mixture, partial vapor pressure may show either a positive or negative deviation from the predicted value of an ideal solution. In this report we derive the deviation from Raoult's law from the heat of mixing, delta H mix, and the molal volume, V, of each of the components of a binary solution. This derivation is then tested for seven sets of combinations of two different solvents, taken at random from the literature. Each set consists of several different ratios of solute-solvent. The correlation between the reported experimental values of the partial vapor pressure of a given component, P1, and the theoretically derived values is excellent. The same derivation is further applied to calculate the solute-solvent interaction parameter, beta 12, independently from the geometric mean assumption of regular solution theory. In a number of cases, especially in hydrocarbon-alcohol mixtures, beta 12 proves to be significantly different from the calculated geometric mean square root beta 11 beta 22 or from the Walker interaction parameter term, K.

Chemical Phenomena↗
PubMed1986

Conformation of nefopam hydrochloride, a novel analgesic.

The solid state structures of (+/-)- and (+)-nefopam hydrochloride (3,4,5,6-tetrahydro-5-methyl-1-phenyl-1H-2,5-benzoxazocine hydrochloride, 1) were determined by single crystal X-ray diffraction analysis. (+/-)-Nefopam hydrochloride gave crystals belonging to monoclinic P21/c space group, and at 298 K: a = 11.766 (1) A, b = 7.741 (1) A, c = 16.907 (3) A, beta = 97.43 (1) degrees, V = 1527.0 (7) A3, Z = 4, R = 0.0336, and Rw = 0.0452. (+)-Nefopam hydrochloride monohydrate gave crystals of the orthorhombic P2(1)2(1)2(1) space group, and at 298 K: a = 9.651 (2) A, b = 19.747 (2) A, c = 8.504 (2) A, V = 1620.7(7) A3, Z = 4, R = 0.0432, and Rw = 0.0690 for the (1S,5S)-model. The diastereoisomer found in the chiral crystal was also found in the solid racemic modification: (1S,5S) in the monohydrate of (+)-1 and (1R,5R)/(1S,5S) in (+/-)-1. 1H and 13C[1H] NMR spectroscopy revealed two distinct, major and minor, N-protonated species in CD2Cl2 solution differing in the stereochemistry of the N-methyl group. The molecular structures of the crystals of (+/-)-1 and (+)-1 X H2O (a) indicate a modified boat-chair conformation of the eight-membered ring with an equatorial N-methyl group, caused by two sp2-hybridized ring atoms, and (b) correspond to the stereochemistry of the minor species in solution.

Crystallization↗
PubMed1986

Structure and development of the surface coat of erythrocytic merozoites of Plasmodium knowlesi.

The surface of extracellular merozoites of P. knowlesi is covered with a coat 15-20 nm thick, made up of clusters of filaments standing erect on the plasma membrane. Filaments have stems 2 nm thick, the peripheral ends of which are complex, branching or ending in long trailing threads. Coat filaments occur on the surface of the parasite in regular rows at an early schizont stage, and persist until well after merozoite release. They are sensitive to trypsin and papain, and bind ethanolic phosphotungstate, indicating a proteinaceous nature. They are also removed by exposure to phosphate-buffered saline. Filaments bear negative charges, binding cationised ferritin throughout the depth of the coat and staining with ruthenium red. They cover the whole merozoite surface and mediate intercellular adhesion at distances of 15-150 nm, membrane to membrane. It is suggested that these filaments correspond to a major merozoite surface protein, and are important in the initial capture of red cells.

Animals↗
PubMed1986

ATP-evoked membrane responses in Xenopus oocytes.

Voltage-clamp technique and intracellular injections of drugs were used to study the adenosine triphosphate (ATP)-evoked depolarizing current response in the Xenopus laevis oocytes. The depolarizing current was comprised of a fast transient component (D1) followed by a late long-lasting component (D2). It was carried mainly by Cl- ions. The depolarizing current was better elicited by ATP and ADP than by AMP or adenosine and was not blocked either by theophylline (0.2 mM) or by quinidine sulphate (1 mM). The D2 current was sometimes masked by an ATP-evoked K+ hyperpolarizing current which was blocked by theophylline and mediated via P1 purinoceptors. This study suggests that the oocyte's membrane embodies at least two different purinoceptor's types, each of these types subserves a different set of ionic channels.

Adenosine Triphosphate↗
PubMed1986

Antigen-nonspecific and specific suppression of lymphokine production in desensitized guinea pigs.

Doubly immunized guinea pigs may be desensitized with respect to delayed hypersensitivity reactions against both antigens (anergy) by injection of large doses of either one. This anergic response therefore has both a specific and nonspecific component. The specific component of desensitization persists longer than the nonspecific one. In the present study, we have explored the mechanism of both antigen-specific and antigen-nonspecific suppression during the later stages of desensitization. Guinea pigs immunized with two antigens, DNP-KLH and DNP-EA, were desensitized with DNP-EA. The lymph node cells obtained from the animals 1 day after desensitization were unable to produce MIF in the presence of either antigen. The cells obtained 3, 5, and 7 days after desensitization were able to generate MIF when stimulated with the non-specific antigen (DNP-KLH), but not with specific antigen (DNP-EA). It was shown that both T- and non-T-cell fractions obtained 1 day after desensitization had the capacity to antigen-nonspecifically suppress MIF production. In contrast, if the cells were obtained 3 or 5 days after desensitization, T cells could inhibit only the antigen-specific production of MIF, while non-T cells were still capable of suppressing antigen-specific and nonspecific MIF production. Interestingly, when these two populations were mixed back again, it was now only suppressive to the specific antigen-induced MIF production. This latter observation indicates that nonspecific suppressor non-T cells may themselves be regulated by suppressor T cells. Furthermore, antigen-specific suppressor T cells were shown to produce soluble factor(s) which inhibited the production of MIF.

Animals↗
PubMed1986

Dual factitious disorder.

The DSM-III classification of factitious disorders encourages artificial separation into disorders with physical and those with psychologic symptoms. Despite documented examples of similar patients who present with psychiatric complaints, Munchausen's syndrome is usually considered a form of chronic factitious physical disorder. Three patients with both factitious physical and psychologic symptoms are presented. These patients illustrate the importance of focusing on the fundamental behavior of assuming the patient role, rather than on the specific category of symptoms. We recommend that the category of symptoms be used as a modifying statement, rather than defining separate disorders.

Adult↗
PubMed1986

Attempts to immunoprecipitate the LHRH precursor synthesized in cell free systems.

In order to determine the molecular weight of the Luteinizing Hormone Releasing Hormone (LHRH) precursor, poly(A)-RNA from rat hypothalami and human placenta were translated in two mRNA dependent cell free translation systems. Total translation products were immunoprecipitated with two antisera that recognized LHRH high molecular weight forms. After SDS-polyacrylamide slab gel electrophoretic analysis of the immunoprecipitated material and fluorography, we detected in both tissues a protein of 50,000 daltons with the No. 1076 antiserum. This peptide was not immunoprecipitated by the No. 743 anti-LHRH antiserum or by non-immune rabbit serum. However, this protein was not displaced by excess LHRH added during the immunoprecipitation and seemed to be present in species where LHRH has not been reported. These data demonstrated that the LHRH mRNA is present in very low amounts in hypothalamus or placenta and that the sensitivity of the assay is not high enough to recognize it.

Animals↗
PubMed1986

The role of lymphokines in neoplastic disease.

In this brief review, we have focused on studies demonstrating the existence of low-molecular-weight lymphokines that modify a number of tumor cell functions. We have found that lymphokine preparations of human or murine origin contain a protein, TMIF, that can reversibly inhibit the migration of a variety of tumor cells. Both serially passaged animal tumors and spontaneous human neoplasms respond to TMIF. Determination of physicochemical characteristics, including molecular weight, enzyme inactivation, monosaccharide inhibition profile, and noncoordinate production by hybridomas, has led to the conclusion that TMIF is distinct from the lymphokines that inhibit the migration of nonneoplastic cells. TMIF can be detected in vivo and can modify the behavior of tumor cells in vivo. In addition, TMIF-containing preparations can inhibit the binding of tumor cells to endothelial monolayers. Although migration inhibition by TMIF is not associated with cytotoxicity, partially purified TMIF preparations are cytostatic for tumor cells. Cytostasis is not the cause of the observed results in the migration assay, and these properties are therefore functionally distinct. These three activities, appearing within a narrow range of molecular weights, different from those of other known lymphokines, suggest the existence of a distinct class of lymphokine mediators with the common function of influencing functional properties of tumor cells. We propose that these mediators be tentatively defined as neomodulins. Further characterization of this set of lymphocyte-derived effector macromolecules will require thorough exploration of their effects on the various functions listed as tumor cell "job descriptions," demonstration of their in vivo efficacy, and purification of the various factors to homogeneity. The neomodulins are likely to have therapeutic potential, since the tumor cell functions that they regulate are those involved in the expression of malignant potential. In addition, studies are under way to determine whether the in vitro responsiveness of tumor cells to these factors might correlate with their in vivo biologic behavior. Finally, detection of TMIF or related lymphokines in serum or urine from patients with neoplasms could be useful in the detection of cancer and/or monitoring of occult tumor metastases and tumor recurrence.

Animals↗
PubMed1986

Social skills and the stress-protective role of social support.

Cross-sectional analyses of data collected from a large sample of incoming college freshmen were used to determine whether the perceived availability of social support protects persons from stress-induced depressive affect; whether social competence, social anxiety, and self-disclosure are responsible for the stress-protective effect of perceived social support; and whether these social skill measures discriminate among persons for whom support will help, hinder, or be ineffective in the face of stress. Prospective analyses based on the original testing (beginning of school year) and 11- and 22-week follow-ups of a randomly selected subsample were used to determine how the same social skill factors influence the development and maintenance of support perceptions and of friendships. Evidence is provided for a stress-buffering role of the perceived availability of social support. The stress-buffering effect is unaffected by controls for the possible stress-protective influences of social anxiety, social competence, and self-disclosure. Although these social skill factors do not discriminate among persons for whom support will help, hinder, or be ineffective, they are prospectively predictive of the development of both social support and friendship formation. These prospective relations between social skills and the development of perceived availability of social support are only partly mediated by number of friends.

Adolescent↗
PubMed1986

Corneal hypoaesthesia in asymptomatic familial distichiasis.

A 3-year-old child, his mother, and his uncle were found to have asymptomatic distichiasis accompanied by corneal hypoaesthesia. Slit-lamp examination of the mother and her brother revealed normal corneas, but bilateral punctate epithelial staining was found in the child. In addition the child suffered from corneal erosion in his left eye due to decreased tear secretion after left occipital craniotomy and C1 laminectomy.

Adult↗