Publications by authors named "Julio D. Martin"

We measured the FIR (Far Infrared) absorbance of a series of organic hydrated sub-nanopores (i.e. pores of the size of several A) containing confined water.

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The behavior of water confined near nonpolar surfaces has important implications for a number of biological phenomena. In this type of confined environment the properties of "hydrophobicity" and "hydrophilicity" are closely related to the structure of the interfacial water, which in turn can depend on temperature in a very subtle way. Although the physical-chemical consequences of this fact have been theoretically addressed to a great extent, the underlying thermodynamic question is still widely discussed.

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Water molecules confined inside narrow pores are of great importance in understanding the structure, stability, and function of water channels. Here we report that besides the H-bonding water that structures the pore, the permanent presence of a significant, fast-moving fraction of incompletely H-bonded water molecules inside the pore should control the free entry and exit of water. This is achieved by means of complementary DSC and solid-state NMR studies.

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Voltage-gated Na+ channels are composed of one alpha subunit and one or more auxiliary beta subunits. A reverse transcription-polymerase chain reaction assay was used to analyse the expression of the nine known alpha subunits (Na(v)1.1-Na(v)1.

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The open-ended hollow tubular structure formed by inclusion of water molecules in the packing of the hydroxyl acid 1 (R1 = CH2OH, R2 = ethyl groups) led to the synthesis and structural study of their unsaturated analogues. In this article we report on a general and practical large-scale synthesis of hydroxyl acids that possess alkenyl and alkynyl appendages. Substitution of the ethyl groups in 1 with unsaturated two-carbon appendages has a different effect on the molecular structure and on the hydrogen-bonding pattern.

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In a model formed by hydroxy acids with a general structure (+/-)-1, we found that solid-state structures depend on steric interactions. Thus, with the exception of molecules 1b and 1e, compounds (+/-)-1a-(+/-)-1m, which possess bulky and conformationally rigid substituents, aggregate by forming tapes and sheets by alternating (+) and (-) subunits held together via carboxylic acid to alcohol hydrogen bonds. Homologue (+/-)-1n with conformationally flexible substituents, which allow conformational deformation gives, by way of the incorporation of water molecules, an efficient hexagonal assembly, which extends to the third-dimension to form tubular H-bonding networks.

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[reaction: see text] The unique solid-state hydration/dehydration properties of the diacid (+/-)-1e in comparison with other homologues of the same family are studied. Hydrophobic enhancement, which is a consequence of the loss of water molecules from (+/-)-1e chains, is a property that can be exploited to achieve organic condensed systems for nonpolar molecules by interstitial van der Waals confinement.

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(1) Studies were undertaken to determine the nature of the receptors mediating contractile effects of tachykinins in the uteri of nonpregnant women, and to analyse the expression of preprotachykinins (PPT), tachykinin receptors and the cell-surface peptidase, neprilysin (NEP), in the myometrium from pregnant and nonpregnant women. (2) The neurokinin B (NKB) precursor PPT-B was expressed in higher levels in the myometrium from nonpregnant than from pregnant women. Faint expression of PPT-A mRNA was detectable in the myometrium from nonpregnant but not pregnant women.

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The incorporation of water molecules into the hydrogen-bonded pattern of condensed organic materials implies an unfavorable entropic tradeoff resulting from water ordering. Here we show for a family of diacids of general structure (+/-)-1 that extended chains of anhydrous or hydrated structures can be prepared by controlling the steric factors that lead to the closest packing of individual components.

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Ring-closing olefin metathesis (RCM) catalyzed by Grubbs's ruthenium benzylidene complex 1 is applied to the synthesis of unsaturated rings ranging in size from seven to thirteen members in trans-fused polyether systems. Reaction occurs with great efficiency in the cyclization of oxepene and oxocene rings, but as ring size increases, yields drop. The influence of the final double bond position is also studied.

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A single, unified convergent strategy for the stereocontrolled synthesis of trans-fused polyethers was developed. It was demonstrated that the epimerization and reductive intramolecular coupling of hydroxy ketones in reactions with silane-Lewis acids (SI-LA) to generate ethers in C-linked oxacycles is affected by its conformational preference in a predictable manner. The obtained results make evident that the influence of hydrogen bonding between a hemiketal hydroxyl and a 1,3-diaxial C-O bond is regular and predictable and that convergent synthesis of trans-fused polyethers may confidently be conducted on driving ring closure to oxane rings under thermodynamic conditions

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