电感耦合等离子体发射光谱法(ICP-AES)测定黑豆和红小豆中15种元素

采用ICP—AES法同时测定黑豆和红小豆中Na,Sn,Ca,Zn,Cu,Mg,Al,Fe,P,K,Si,Se,Ba,Mn,M015种元素含量,并对各元素进行了加标回收实验,黑豆和红小豆中各元素的平均回收率在93．11％～102．15％,相对标准偏（RSD）在0．83％0～2．8％,检出限介于0．11～14．09Fg／L。建立了简便、快速、准确和稳定的测定黑豆和红小豆中元素的测定方法。结果显示在黑豆和红小豆中K,Ca,P,Mg,Mn,Fe,Zn等常量元素和微量元素含量较高。红小豆中Ca,Mg,Fe,Zn等营养元素的含量较黑豆中的高。     

无机钙材料在石灰岩文物表面防护中的应用

由于碳酸盐矿物的质地特点,石灰岩文物在露天环境中极易发生表面溶蚀,其上赋存文化信息的文字、纹饰和符号等雕刻痕迹也随之湮灭,对其文物价值造成了严重减损。从耐候性和兼容性角度考虑,无机保护材料显然更适合于石灰岩文物的表面防护处理。近年来,基于草酸钙、磷灰石和碳酸钙等钙基材料的石灰岩文物表面防护研究逐渐兴起并开始走向应用。本文就上述钙基保护材料的特点、防护膜制备和应用实践等做了归纳和评述,以期为石灰岩文物保护研究提供参考和借鉴。     

Using dangling bond density to characterize the surface energy of nanomaterials

Taking f.c.c Ag, Al, Au, Ir, Pd, Pt, Rh and b.c.c Cr, Fe, Mo, Nb, Ta, V, W as examples, the energetic and bonding features of unrelaxed cubic nanoparticles were investigated by the modified embedded atom method. The surface free energy increases almost inversely with the decreasing feature sizes. This is the essential reason for the fantastic microstructures and distinct properties observed at the nanometer scale. According to the analysis on atomic bonding states, we further found that the size‐dependent surface energy is directly associated with the dangling bond density. Summing up these two aspects, the dangling bond density, a microscopic parameter, is believed to be one of the intrinsic physical quantities characterizing the structures and properties of nanomaterials. Copyright © 2007 John Wiley & Sons, Ltd.     

Trace element determination in tomato puree using particle induced X-ray emission and Rutherford backscattering

Particle induced X-ray emission (PIXE) and Rutherford backscattering spectrometry (RBS) were used to determine the concentrations of trace elements in samples of 12 tomato puree brands sold in the Mexican market. While RBS offered information about the main elements present in the matrix, PIXE gave results on trace elements. As a whole, data for 17 elements (C, N, O, Na, Mg, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, and Zn) were obtained. To evaluate the results, a comparison with brands from USA, Japan, Colombia, and Chile was carried out, using tomato purees produced following the domestic technology recipe. Additionally, the results were considered in the light of the Codex Alimentarius and the Mexican standard. It was found that all of the brands fall within the limits established by these standards, being of the same order of magnitude as the foreign brands. This revised version was published online in July 2006 with corrections to the Cover Date.     

Photoinduced ferrimagnetic systems in Prussian blue analogues C(I)xCo4[Fe(CN)6]y (C(I) = alkali cation). 3. Control of the photo- and thermally induced electron transfer by the [Fe(CN)6] vacancies in cesium derivatives.

We synthesized a series of CoFe Prussian blue analogues along which we tuned the amount of cesium cations inserted in the tetrahedral sites of the structure. Structure and electronic structure have been investigated, combining XANES, infrared spectroscopy, powder X-ray diffraction experiments, and magnetization measurements. The change of the magnetization induced by light along the series shows that the efficiency of the photoinduced magnetization, evidenced a few years ago in similar compounds by Hashimoto et al. (Sato, O.; Iyoda, T.; Fujishima, A.; Hashimoto, K. Science 1996, 272, 704-705; Sato, O.; Einaga, Y.; Iyoda, T.; Fujishima, A.; Hashimoto, K. J. Electrochem. Soc. 1997, 144, L11-L13; Sato, O.; Einaga, Y.; Iyoda, T.; Fujishima, A.; Hashimoto, K. J. Phys. Chem. B 1997, 101, 3903-3905; Einaga, Y.; Ohkoshi, S.-I.; Sato, O.; Fujishima, A.; Hashimoto, K. Chem. Lett. 1998, 585-586; and Sato, O.; Einaga, Y.; Fujishima, A.; Hashimoto, K. Inorg. Chem. 1999, 38, 4405-4412), depends on a compromise between the number of excitable diamagnetic pairs and the amount of [Fe(CN)6] vacancies giving the network flexibility. Besides the efficiency of the photoinduced process, the amount of [Fe(CN)6] vacancies also controls a thermally induced electron transfer.     

128例脑性瘫痪血钙、锌、铁、铜、镁元素分析

为探讨小儿脑性瘫痪(CP)体内微量元素的变化,测定了128例脑性瘫痪患者血钙、锌、铁、铜、镁含量,随机选择128例正常儿童进行对照分析。结果表明,两组病例血锌、铜、镁均在正常范围,脑瘫组血钙56例、铁45例低于正常参考值,健康组血钙16例、铁11例低于正常参考值。经统计学处理,两组病例中血钙、铁、铜、镁含量具有显著性差异(P<0.05),血锌无显著性差异(P>0.05)。提示脑瘫儿童血钙、铁、铜、镁含量均低于正常儿童,补充钙、铁、镁等可能有利于脑瘫康复。     

Determination of impurities in nuclear fuel element components by neutron activation analysis

Neutron activation analysis methods for the determination of impurities in zirconium cladding material and uranium oxide are described. Detection limits for the elements Al, Cd, Cr, Co, Cu, Hf, Fe, Mn, Ni, W and U in zirconium are below that required by the ASTM B 352-79 standard. The method has been tested on the NIST SRM 360a Zircaloy-2 from which the elements Na, Mg, Al, Ca, V, Cr, Fe, Co, Ni, Cu, Eu and U have been detected. The values for Cr, Fe, Ni and Cu are compared with the certified values. A method for the pre-irradiation separation of the elements Mg, Na, Al, K, Sc, Ca, V, Mn, Cr, Fe, Co, Cu, Zn, Rb, Zr, Cd, Cs, REE and Hf from uranium has been developed. A neutron activation analysis method for the determination of those elements in uranium is described. The method is tested by the analysis of the IAEA reference sample SR-54/64. The elements Al, Mn, V, Cu, Cr, Co, Ni and Fe have been detected and the results compared with the certified values.     

The capability of neutron activation for trace element analysis in sea water and sediment samples of the Northern Adriatic Sea

In a framework of a more intensive study of the oceanographic phenomenology of the Northern Adriatic Sea, recently undertaken by the O. G. S. of Trieste, the present paper provides some insight into the determination of trace elements in sea water and bottom sediment matrices. Sampling procedure using continuous pumping and filtering and neutron activation analytical techniques are presented and the obtained results briefly discussed. Accounting for the physiography of the basin, for the oceanographic processes and for the different freshwater input, several samples were collected of filtered water in order to set up their properties. Results were obtained throughout the settlement only for long-lived radionuclides based on routine neutron activation: Cr, Ag, Co, Cs, Rb, Sb, Sc, Sr, Zn, U. For each of them, the concentration range was determined and discussed. Results indicate that the Cs, Rb, Sr and U concentration range is readily comparable with that assessed at open seas. On the contrary, for the other elements such as Cr, Ag, Co, Sc, Sb and Zn concentrations are noticeably higher than those found at open seas, mainly as far as samples collected near the sea bottom are concerned. The concentration increase is surely related to the burden of pollutants suffered by rivers. Moreover, the positive concentration gradient experienced toward the bottom, is fully in agreement with the estuarine character of the investigated area and in accordance with the strong decomposition of organic matter taking place in the bottom layer of the basin. Finally, the complexity of the sedimentary pattern in the Northern Adriatic renders it difficult to properly define the element concentration in bottom sediment. Only four samples were chosen as representative of the different sediments and analysed. Long-lived elements obtained are: Ce, Co, Cs, Cr, Rb, Sc, Tb, Yb. Their concentration was found to be related to the geochemical features of the activated matrix.     

Character of the reaction of di- and polynucleotides with some pesticides

Lontrel, Sencor, Roundup, Kusagard, Tachigaren, Tilt, and Sethoxydim, as well as the bidentate Cu, Co, Ni, Mo, and Fe complexes of the herbicide Lontrel form molecular complexes with adenine heterocyclic compounds containing di- and polynucleotides. Sencor forms the strongest complexes, and Tilt has the lowest complexing constant. Lontrel, Sencor, Basagran, and Roundup totally destroy the cooperative character of the double helix of native DNA. The overall effect of the pesticides on nucleotides is determined both by the complexing constant with the purine base and by the capacity of the molecule of the pesticide to reach the reaction side located in the depth of the twisted double helix of DNA and RNA.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 1984–1989, September, 1989.     

Electronic structures and chemical bonding in 4d transition metal monohalides

Bond distances, vibrational frequencies, dipole moments, dissociation energies, electron affinities, and ionization potentials of MX (XM = Y-Cd, X = F, Cl, Br, I) molecules in neutral, positively, and negatively charged ions were studied by density functional method, B3LYP. The bonding patterns were analyzed and compared with both the available data and across the series. It was found that besides ionic component, covalent bonds are formed between the 4d transition metal s, d orbitals, and the p orbital of halogen. For both neutral and charged molecules, the fluorides have the shortest bond distance, iodides the longest. Although the opposite situation is observed for vibrational frequency, that is, fluorides have the largest value, iodides the smallest. For neutral and anionic species, the dissociation energy tends to decrease with the increasing atomic number from Y to Cd, suggesting the decreasing or weakening of the bond strength. For cationic species, the trend is observed from Y to Ag.     

基于无基底扣除的数据趋势累积谱峰检测算法

谱峰的检测分析在色谱技术研究中具有十分重要的作用,但在色谱数据采集、传输的过程中,不同程度的噪声干扰给谱峰检测带来了极大的困难.目前传统的谱峰检测算法普遍通过基底扣除的方式对谱峰的形态进行预定义,将谱峰分为单峰、重叠峰等多个种类.针对不同种类的谱峰采用不同的检测方法,这就导致了传统的谱峰检测算法具有高复杂度、低自动化程...     

The retention of 1,1-dimethylhydrazine and its decomposition products on alkyl-grafted silica gels under the ion pair chromatography conditions

The influence of eluent composition (the nature and concentration of the ion-pair reagent, medium pH, the concentration of the buffer solution, and the content of acetonitrile) on the retention of asymmetric dimethylhydrazine and its decomposition products on hydrophobized silica gels under the ion pair chromatography conditions was studied. It was shown that, for these sorbates, the influence of ion-pair reagents can be described correctly in terms of stoichiometric models. Empirical dependences of the retention of the components studied on the concentration of the buffer solution and the volume concentration of acetonitrile were determined. Conditions for the separation of the components were suggested. Original Russian Text ? A.D. Smolenkov, S.A. Ponomarenko, O.A. Shpigun, 2009, published in Zhurnal Fizicheskoi Khimii, 2009, Vol. 83, No. 3, pp. 565–574.     

Quenching of tryptophan (1)(pi,pi*) fluorescence induced by intramolecular hydrogen abstraction via an aborted decarboxylation mechanism

CASSCF computations show that the hydrogen-transfer-induced fluorescence quenching of the (1)(pi,pi*) excited state of zwitterionic tryptophan occurs in three steps: (1) formation of an intramolecular excited-state complex, (2) hydrogen transfer from the amino acid side chain to the indole chromophore, and (3) radiationless decay through a conical intersection, where the reaction path bifurcates to a photodecarboxylation and a phototautomerization route. We present a general model for fluorescence quenching by hydrogen donors, where the radiationless decay occurs at a conical intersection (real state crossing). At the intersection, the reaction responsible for the quenching is aborted, because the reaction path bifurcates and can proceed forward to the products or backward to the reactants. The position of the intersection along the quenching coordinate depends on the nature of the states and, in turn, affects the formation of photoproducts during the quenching. For a (1)(n,pi*) model system reported earlier (Sinicropi, A.; Pogni, R.; Basosi, R.; Robb, M. A.; Gramlich, G.; Nau, W. M.; Olivucci, M. Angew. Chem., Int. Ed. 2001, 40, 4185-4189), the ground and the excited state of the chromophore are hydrogen acceptors, and the excited-state hydrogen transfer is nonadiabatic and leads directly to the intersection point. There, the hydrogen transfer is aborted, and the reaction can return to the reactant pair or proceed further to the hydrogen-transfer products. In the tryptophan case, the ground state is not a hydrogen acceptor, and the excited-state hydrogen transfer is an adiabatic, sequential proton and electron transfer. The decay to the ground state occurs along a second reaction coordinate associated with decarboxylation of the amino acid side chain and the corresponding aborted conical intersection. The results show that, for (1)(pi,pi*) states, the hydrogen transfer alone is not sufficient to induce the quenching, and explain why fluorescence quenching induced by hydrogen donors is less general for (1)(pi,pi*) than for (1)(n,pi*) states.     

A proton-shuttle mechanism mediated by the porphyrin in benzene hydroxylation by cytochrome p450 enzymes

Benzene hydroxylation is a fundamental process in chemical catalysis. In nature, this reaction is catalyzed by the enzyme cytochrome P450 via oxygen transfer in a still debated mechanism of considerable complexity. The paper uses hybrid density functional calculations to elucidate the mechanisms by which benzene is converted to phenol, benzene oxide, and ketone, by the active species of the enzyme, the high-valent iron-oxo porphyrin species. The effects of the protein polarity and hydrogen-bonding donation to the active species are mimicked, as before (Ogliaro, F.; Cohen, S.; de Visser, S. P.; Shaik, S. J. Am. Chem. Soc. 2000, 122, 12892-12893). It is verified that the reaction does not proceed either by hydrogen abstraction or by initial electron transfer (Ortiz de Montellano, P. R. In Cytochrome P450: Structure, Mechanism and Biochemistry, 2nd ed.; Ortiz de Montellano, P. R., Ed.; Plenum Press: New York, 1995; Chapter 8, pp 245-303). In accord with the latest experimental conclusions, the theoretical calculations show that the reactivity is an interplay of electrophilic and radicalar pathways, which involve an initial attack on the pi-system of the benzene to produce sigma-complexes (Korzekwa, K. R.; Swinney, D. C.; Trager, W. T. Biochemistry 1989, 28, 9019-9027). The dominant reaction channel is electrophilic and proceeds via the cationic sigma-complex,( 2)3, that involves an internal ion pair made from a cationic benzene moiety and an anionic iron porphyrin. The minor channel proceeds by intermediacy of the radical sigma-complex, (2)2, in which the benzene moiety is radicalar and the iron-porphyrin moiety is neutral. Ring closure in these intermediates produces the benzene oxide product ((2)4), which does not rearrange to phenol ((2)7) or cyclohexenone ((2)6). While such a rearrangement can occur post-enzymatically under physiological conditions by acid catalysis, the computations reveal a novel mechanism whereby the active species of the enzyme catalyzes directly the production of phenol and cyclohexenone. This enzymatic mechanism involves proton shuttles mediated by the porphyrin ring through the N-protonated intermediate, (2)5, which relays the proton either to the oxygen atom to form phenol ((2)7) or to the ortho-carbon atom to produce cyclohexenone product ((2)6). The formation of the phenol via this proton-shuttle mechanism will be competitive with the nonenzymatic conversion of benzene oxide to phenol by external acid catalysis. With the assumption that (2)5 is not fully thermalized, this novel mechanism would account also for the observation that there is a partial skeletal retention of the original hydrogen of the activated C-H bond, due to migration of the hydrogen from the site of hydroxylation to the adjacent carbon (so-called "NIH shift" (Jerina, D. M.; Daly, J. W. Science 1974, 185, 573-582)). Thus, in general, the computationally discovered mechanism of a porphyrin proton shuttle suggests thatthere is an enzymatic pathway that converts benzene directly to a phenol and ketone, in addition to nonenzymatic production of these species by conversion of arene oxide to phenol and ketone. The potential generality of protonated porphyrin intermediates in P450 chemistry is discussed in the light of the H/D exchange observed during some olefin epoxidation reactions (Groves, J. T.; Avaria-Neisser, G. E.; Fish, K. M.; Imachi, M.; Kuczkowski, R. J. Am. Chem. Soc. 1986, 108, 3837-3838) and the general observation of heme alkylation products (Kunze, K. L.; Mangold, B. L. K.; Wheeler, C.; Beilan, H. S.; Ortiz de Montellano, P. R. J. Biol. Chem. 1983, 258, 4202-4207). The competition, similarities, and differences between benzene oxidation viz. olefin epoxidation and alkanyl C-H hydroxylation are discussed, and comparison is made with relevant experimental and computational data. The dominance of low-spin reactivity in benzene hydroxylation viz. two-state reactivity (Shaik, S.; de Visser, S. P.; Ogliaro, F.; Schwarz, H.; Schr?der, D. Curr. Opin. Chem. Biol. 2002, 6, 556-567) in olefin epoxidation and alkane hydroxylation is traced to the loss of benzene resonance energy during the bond activation step.     

无机钙材料在石灰岩文物表面防护中的应用

由于碳酸盐矿物的质地特点,石灰岩文物在露天环境中极易发生表面溶蚀,其上赋存文化信息的文字、纹饰和符号等雕刻痕迹也随之湮灭,对其文物价值造成了严重减损。从耐候性和兼容性角度考虑,无机保护材料显然更适合于石灰岩文物的表面防护处理。近年来,基于草酸钙、磷灰石和碳酸钙等钙基材料的石灰岩文物表面防护研究逐渐兴起并开始走向应用。本文就上述钙基保护材料的特点、防护膜制备和应用实践等做了归纳和评述,以期为石灰岩文物保护研究提供参考和借鉴。     

Advances in the chemistry of tetrazoles (review)

The review is devoted to the newest advances in the chemistry of tetrazoles. New data on the electronic structures, crystal structures, and dipole moments are presented successively. The electronic, vibrational, NMR, and mass spectra are discussed. Data on the acid-base properties and tautomerism of tetrazoles are presented. Numerous methods for the preparation of tetrazole and mono- and disubstituted tetrazoles are reported. The chemical properties of tetrazoles, viz., electrophilic substitution at the ring carbon atom, nucleophilic substitution, alkylation, electrophilic and nucleophilic substitution in the side chain, and the effect of oxidizing and reducing agents, are discussed. Reactions that lead to cleavage of the tetrazole ring, viz., acylation and thermolysis, are examined separately. New data on the use of tetrazoles in medicine, biology, agriculture, the manufacture of polymeric materials, etc. are presented.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1299–1326, October, 1981.     

Reflections on the Philosophy of Chemistry and a Rallying Call for Our Discipline

Biology in the popular mind remains tied to the doctrines of the struggle forsurvival and the survival of the fittest. Physics is linked to the heat deathof the universe – the inexorable march towards greater disorder,increasing entropy. Our field, on the other hand, focuses on orderedstructures, molecules and crystals, and their aggregates, and what holdsthem together. The philosophy of chemistry is centered on affinity,cohesion, the architecture of the very small, attraction, harmony, and, ifyou permit, beauty. Our discipline is the voice of the twenty-first century,a message, a clarion call of life, of hope. This paper addresses failures ofreductionist and deterministic claims in the face of the cussedness ofchemical facts. It will examine uncertainty principles, Edmund Whitaker'spostulates of impotence, Gerald Holton's themata, Isaiah Berlin's warning –and the wisdom of the Chinese. We can teach the world the need for humilityin the face of the wonder and mystery of our world. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effect of Cr(VI) anions on adsorption and desorption behavior of Cu(II) in the colloidal systems of two authentic variable charge soils

Heavy metals in wastes exist as multiple pollutants. The study of the interactions between multiple pollutants and soils should be of significance in practice. In the present study, the effect of chromate on adsorption and desorption behavior of Cu(II) in two variable charge soils was investigated, with the emphasis on the adsorption and desorption equilibria of Cu(II). The results showed that chromate can affect adsorption and desorption of Cu(II) in the colloidal systems of two variable charge soils. The extent of the effect was related to the initial concentrations of chromate and Cu(II), the system pH, and the nature of the soils. The presence of chromate led to an increase in the adsorption of Cu(II). For example, in the presence of 0.5, 0.8, 1.0, and 1.5 mmol L(-1) of chromate, for the rhodic ferralsol the adsorption of Cu(II) increased by 15.3, 18.0, 19.0, and 20.2%, respectively. For the hyperrhodic ferrasol, the corresponding figures were 11.9, 17.0, 20.3, and 26.1%, respectively. The presence of chromate also caused an increase in the desorption of Cu(II). For instance, in the presence of 0.5, 1.0, and 1.5 mmol L(-1) of chromate, the desorption for the rhodic ferralsol increased by 16.9, 27.5, and 34.1%, respectively. For the hyperrhodic ferralsol, the corresponding figures were 18.1, 35.6, and 51.4%, respectively. The increments of the adsorption and desorption increased with the increase in equilibrium concentration of Cu(II) in the solution. For instance, when the equilibrium concentrations were 0.5, 1.0, 1.5, and 2.0 mmol L(-1), the increments for the rhodic ferralsol were 2.5, 3.2, 3.3, and 3.0 mmol kg(-1), respectively. For the hyperrhodic ferralsol, the corresponding figures were 2.9, 3.5, 4.0, and 4.2 mmol kg(-1), respectively. The effect of chromate for the hyperrhodic ferralsol was greater than that for the rhodic ferralsol. This is caused by the difference in the content of iron oxides for the two soils. The increments of the adsorption and the desorption of Cu(II) increased with the rise in pH, reaching a maximum value, and then decreased. It can be assumed that the increment of the adsorption was caused by the change in surface charge of the soils induced by the adsorption of chromate and the cooperative adsorption of chromate adsorbed and Cu(II). The increase of electrostatically adsorbed Cu(II) was responsible for the increase in the desorption of Cu(II).     

Electrokinetic investigation of surfactant adsorption

Fuerstenau [D.W. Fuerstenau, in: M.L. Hair (Ed.), Dekker, New York, 1971, p. 143] has already discussed the role of hydrocarbon chain of surfactants, the effect of alkyl chain length, chain structure and the pH of the solution on the adsorption process of surfactants. Later Kosmulski [M. Kosmulski, Chemical Properties of Material Surfaces, Surfactant Science Series, vol. 102, Dekker, New York, Basel, 2001] included the effect of surfactant concentration, equilibration time, temperature and electrolyte in his approaches. Certainly, the character of the head groups of the surfactant and the properties of the adsorbent surface are the basis for the adsorption process. Different surfactants and adsorbents cause different adsorption mechanisms described firstly by Rosen [M.J. Rosen, Surfactants and Interfacial Phenomena, second ed., Wiley, New York, 1989]. These adsorption mechanisms and their influencing factors were studied by electrokinetic investigations. Here only changes of the charges at the surfaces could be detected. To control the results of electrokinetic investigations they were compared with results from ellipsometric measurements. In the case of surfactant adsorption the chain length was vitally important. It could be shown by the adsorption of alkyl trimethyl ammonium bromides onto polymer films spin coated at wafer surfaces. The influence of the chain length depending on surface properties of the polymer film was studied. Streaming potential measurements were applied for these investigations. The obtained results enabled us to calculate the molar cohesive free energy per mol of CH2-group in the alkaline chain of the surfactant if all other specific adsorption effects were neglected.     

Protein-matrix coupling/uncoupling in "dry" systems of photosynthetic reaction center embedded in trehalose/sucrose: the origin of trehalose peculiarity

Trehalose is a nonreducing disaccharide of glucose found in organisms, which can survive adverse conditions such as extreme drought and high temperatures. Furthermore, isolated structures, as enzymes or liposomes, embedded in trehalose are preserved against stressing conditions [see, e.g., Crowe, L. M. Comp. Biochem. Physiol. A 2002, 131, 505-513]. Among other hypotheses, such protective effect has been suggested to stem, in the case of proteins, from the formation of a water-mediated, hydrogen bond network, which anchors the protein surface to the water-sugar matrix, thus coupling the internal degrees of freedom of the biomolecule to those of the surroundings [Giuffrida, S.; et al. J. Phys. Chem. B 2003, 107, 13211-13217]. Analogous protective effect is also accomplished by other saccharides, although with a lower efficiency. Here, we studied the recombination kinetics of the primary, light-induced charge separated state (P(+)Q(A)(-)) and the thermal stability of the photosynthetic reaction center (RC) of Rhodobacter sphaeroides in trehalose-water and in sucrose-water matrixes of decreasing water content. Our data show that, in sucrose, at variance with trehalose, the system undergoes a "nanophase separation" when the water/sugar mole fraction is lower than the threshold level approximately 0.8. We rationalize this result assuming that the hydrogen bond network, which anchors the RC surface to its surrounding, is formed in trehalose but not in sucrose. We suggest that both the couplings, in the case of trehalose, and the nanophase separation, in the case of sucrose, start at low water content when the components of the system enter in competition for the residual water.