On the study by D.S.C. of the unexpected ice melting at 0°C of emulsified aqueous saline solutions

Firstly, the behavior of droplets (Φ ≈ 1μm) of aqueous saline solutions dispersed within an emulsifying medium and subjected to steady cooling and heating is described. Droplets undergo freezing around a temperature T¹(x) and partial ice melting and total salt melting at the eutectic temperature T_E. This melting is followed by progressive melting of the remaining ice which ceases when the equilibrium temperature (T_e(x)) ice ⇆ solution is reached. Between T_e and T¹ the droplets are undercooled. Secondly, the results obtained when water crystallization occurs versus time at a fixed temperature _C, such as T¹(x) < > _C < T_e(x) are reported. During heating following crystallization at Θ_C, an unusual ice melting at 0° and/or ice melting ending at T & >; T_e(x) is noticed on the thermogram obtained by differential scanning calorimetry of the emulsion. This shows that pure ice or at all events less concentrated solutions must be present within the emulsion. A possible mechanism of crystallization at Θ_C is proposed.     

RECIPROCAL A.C.OSCILLOPOLAROGRAM

In this paper a new electrochemical method“Reciprocal a.c.oscillololarography”is discussed.Both principle and experimental work aredescribed.     

Total synthesis of erythronolide B. 1. Skeleton assembly in (C9C13) + (C7C8) + (C1C6) sequence.

Erythronolide B has been synthesized starting from levoglucosan.     

Design criteria for molecular mimics of fragments of the β-turn. 1. Cα atom analysis

Peptides represent an extensive class of biologically active molecules. They may be used as leads in the development of novel therapeutic agents provided the pharmacophoric information present within them can be translated into non-peptide analogs that lack the peptide backbone and are stable to proteolysis. This is the rationale for peptidomimetic drug design. Frequently, the -turn has been implicated as a conformation important for biological recognition of peptides. Empirical evidence from known peptidomimetics, coupled with a theoretical model of peptide binding and the observation that glycine and proline residues are common within the -turn, has suggested the design of molecules to mimic placement of between two and four of the side-chains. The moderate number of different -turn conformations, combined with the combinatoric nature of side-chain selection complicates the procedure. In this paper, cluster analysis has been used to classify the arrangement of C_{_} atoms about the various fragments of the -turn. Recombination of the observed patterns provides a general model for the -turn which may be used as an effective screen for potential peptidomimetic scaffolds in chemical databases.     

Two New C—glucoside Flavonoids from Leaves of Crataegus pinnatifida Bge. var. major N.E.Br.

Two new C-glucoside flavonoids,namely 8-C-β-D-（2″-O-acetyl) glucofuranosyl apigenin and 3″-O-acetylvitexin, were isolated from beaves of Crataegus pinnatifida Bge. var. major N.E.Br.Their structures were elucidated by the spectroscopic means and chemical evidence.     

Studies on Chemical Composition of Anemone Altaica C.A.May (Ⅱ)

A new dispirolactone compound,C10H12O6 m.p.224-226℃,wasisolated from the ethyl acetate extract of the roots of anemone aJ-taica C.A.May,the Chinese medicinal herb,by using Si gel column chromatography.Its structure was determined as: 1,6,9,13-tetra-oxadispiro[4,2,4,2]tetradecane-2,10-dione by means of IR,NMR,MS spectra and X-ray diffraction analysis.     

Highly Deoxygenated Sugars. II. Synthesis of Chiral Cyclopentenes via Novel Carbocyclization of C‐4 Branched Deoxysugars

Tri‐O‐acetyl‐d‐glucal (1) was converted via Ferrier type II rearrangement with high α‐selectivity to 2,3‐unsaturated methyl glycosides 2a and 2b using ferric chloride as the catalyst. Palladium induced allylic substitution with sodium tert‐butylacetoacetate as a nucleophile leads to C‐4 branched sugars. Subsequent hydrogenation followed by treatment with trifluoroacetic acid affords the highly functionalized chiral cyclopentene derivative 5a as a versatile chiral building block for cyclopentanoids.     

C.A.索引图表分析

一、C.A.有哪些索引美国《化学文摘》(Chemical Abstracts——C.A.)从1907年创刊至今七十余年,索引从少到多,从简单     

Preparation of the C1∼C10 fragment of carbonolide B. A relay approach to carbomycin B

Reaction of methyl 2,3-anhydro-5,6-O-cyclohexylidene-β-D-allofuranoside with 2-methyl-2-propenylmagnesium chloride selectively gave methyl 5,6-O-cyclohexylidene-3-deoxy-3-C-(2-methyl-2-propenyl)-β-D-glucofuranoside, which was converted into the C1∼C10 fragment of carbonolide B by a sequence of reactions involving hydroboration of the prochiral double bond, oxidative cleavage between C5C6, and subsequent stereoselective three-carbon elongation at the C5 position.     

Total synthesis of erythronolide B. 2. Skeleton assembly in (C5C9) + (C3C4) + (C1C2) + (C11C13) sequence.

Erythronolide B has been synthesized starting from levoglucosan.     

Thermodynamics of aqueous gallium chloride. Heats of solution and dilution at 25°C

The heat of solution of GaCl₃ and heats of dilution of single GaCl₃ solutions in water and of mixed GaCl₃−HCl solutions in HCl solutions (with a fixed HCl concentration of 0.1337 mol-kg⁻¹ HCl) up to 4 mol-kg⁻¹ GaCl₃ were measured at 25°C. While in the acid solutions hydrolysis is suppressed to below 0.5% of total gallium concentration, the measurements in water allow evaluation of the effect of hydrolysis on the relative enthalpy. The Pitzer interaction model for excess properties of aqueous electrolytes was used to interpret the change in relative enthalpy with concentration. Pitzer parameters were derived by statistical inference using ridge regression. Their physical significance is supported by the heat of solution data. The measurements yield the following results for standard heats of formation and Pitzer parameters for the relative molar enthalpy at 25°C: With these parameters the overall variance in the partial molar heat of solution at infinite dilution, extrapolated from the present experiments, is minimized to 0.35 kJ²-mol⁻², while the experimental apparent molar heats of dilution are reproduced on average within 2.7 kJ-mol⁻¹.     

A New Steroidal Alkaloid from Bulbs of Fritillaria Hupehensis Hsiao et K. C. Hsia

Fritillaria hupehensis Hsiao et K. C. Hsia is a liliaceous plant growing in the southwest district of Hubei Province, China. Its bulbs have been recorded in the Pharmacopoeia of the People‘s Republic of China as one of the principal traditional Chinese herbs named “Hubeibeimu”.     

FREQUENCY-SPECTRUM ANALYSIS OF A.C.OSCILLOPOLAROGRAM

Application of Frequency-Spectrum analysis to a.c,oscillopolarogram using Fourier transform technique is given in this paper.Harmonic equations of E-t curve of base solution are derived.The measurementof concentration of the depolarizer by means of the second and third harmoniopotentials were also described.     

A note to the article “polarographic reduction of germanium” by A.K. Dasgupta and C.K.N. Nair

The nature of the two reduction waves of tetravalent germanium in ammonia-ammonium chloride buffer is described. Contrary to the statement of dasgup'ta and NAIR1 only the height of the first diffusion current should be used for analytical purposes. The second wave corresponds to a catalytic hydrogen evolution. The use of cthylenediaminetetra-acetic acid of pH 6–8 for the analysis of germanium is preferable².     

A new compound with cytotoxic activities from the leaves of Panax ginseng C.A. Meyer

A new compound, 3,6,20（S）-trihydroxy- 12,23-epoxydammar-24-ene,6,20-di-O-β-D-glucopyranoside （1）, was isolated from the leaves of Panax ginseng C.A. Meyer, whose structural elucidation was carried out by means of spectral analysis （including IR, HR- FAB-MS and NMR）. This compound showed the moderate cytotoxic activities against U937 and HeLa cells by using the MTT method.