IN THE PRIME OF HIS LIFE
A decagonal mini-crossword
Noam D. Elkies, 19 February 2014; improved by George Barany

SOLUTION

1 2 3 4 5 6 7
H E LIX    1   Alpha _____ (protein-structure motif)
E LIX I R    2   Bordeaux wine, to Dr. Dulcamara
LIX I V I A T E    3   Extract by washing or percolation
R I  B   B   O   N     4   _____ diagram (protein-structure visualization)
A B O V E    5   _____ average (like every child in Lake Wobegon)
T O V    6   “Mazel ___!” (“Happy 59th birthday!”)
E N E    7   Mercedes-Benz suffix, to a jocular organic chemist

No Down clues: this decagon is symmetrical about the main diagonal, and the same words appear Across and Down.

The first version of this puzzle (with a different solution) was hastily constructed for George Barany(=GB)’s 59th birthday (59 happens to be a prime number, whence the title’s pun); the present version was greatly improved by GB’s suggestions, as further detailed below. This might be my first attempt at a rebus puzzle, here using the Roman numeral LIX for 59. Not many common words contain this string, but fortunately three of them are appropriate to GB’s interests and interlock properly (even allowing a fortuitous link with RIBBON), albeit requiring a rare grid shape.

As usual with these mini-puzzles, further (and proLIX) construction and clue notes follow in the small print.

The RIBOSE or RIBBON link would not be available had the first word been FE[LIX] as in Mendelssohn. The other common words I found were pro[lix] and bol[lix], neither of which is appropriate to a birthday present. Alas I couldn’t use SA[LIX] (botanical name for the willow), as in salicylic acid = precursor of aspirin. xwordinfo also gives a few proper/trade names such as B[LIX]EN, MUES[LIX], and NETF[LIX]. And A[LIX], which together with SA[LIX] and [LIX] itself would make this a triangular micropuzzle instead of a decagonal minipuzzle.
1: See for instance this Wikipedia page. Originally I clued HE[LIX] via RNA, rather than DNA which is famously a double helix; I had naïvely jumped to the conclusion that a single RNA strand, being much like half of DNA (but for the de(s)oxygenation indicated by the acronym’s first letter), would be a single helix. Turns out that RNA, unlike DNA, has a much more complicated and sequence-dependent geometry, making that cluing route problematic. Fortunately GB noticed that protein structures also have helical motifs and fortuitously allow for a different link with the 4th word of the grid (which used to be RIBOSE as in the R of RNA) with thematic opportunities for the remaining entries 5–7.
2: As revealed in an aside to the audience in Donizetti’s blockbuster comic opera L'elisir d'amore (The Elixir of Love).
3: Well what else starts with LIX!? At least GB is a chemist.
4: a.k.a. Richardson Diagram, named for its developer. The Wikipedia page gives this example, hand-drawn by Richardson herself, showing both α-helices and β-sheets.
5: From the standard closing monologue of Minnesotan Garrison Keillor’s radio show A Prairie Home Companion. This famous signoff made the fictional Minnesota town of Lake Wobegon the eponym of the Lake Wobegon effect of illusory superiority.
6: To be sure, “Mazel Tov!” (a Yiddish/Hebrew phrase with a curious and circuitous etymology) isn’t specifically a birthday greeting, let alone one specific to a 59th birthday. But this phrasing of the clue may also help solvers other than GB diagnose and/or corroborate the rebus.
7: Cluing path suggested by GB and enthusiasically accepted by NDE. See for instance this instance and prolixplanation of the “Mercedes-Benzene” joke.
Hey, the solutions are almost in alphabetical order! But alas not quite: even if I assign “_____” a reading such as “[fill in the blank]” to fit between “extract” and “ “Mazel” ”, clue 5 would alphabetically precede clue 4.